GUT FEELINGS - UNCONSCIOUS INTELLIGENCE - Gut Feelings: The Intelligence of the Unconscious - Gerd Gigerenzer

Gut Feelings: The Intelligence of the Unconscious - Gerd Gigerenzer (2007)


We know more than we can tell.

—Michael Polanyi


The heart has its reasons of which reason knows nothing.

—Blaise Pascal

We think of intelligence as a deliberate, conscious activity guided by the laws of logic. Yet much of our mental life is unconscious, based on processes alien to logic: gut feelings, or intuitions. We have intuitions about sports, friends, which toothpaste to buy, and other dangerous things. We fall in love, and we sense that the Dow Jones will go up. This book asks: Where do these feelings come from? How do we know?

Can following your gut feelings lead to some of the best decisions? It seems naive, even ludicrous, to think so. For decades, books on rational decision making, as well as consulting firms, have preached “look before you leap” and “analyze before you act.” Pay attention. Be reflective, deliberate, and analytic. Survey all alternatives, list all pros and cons, and carefully weigh their utilities by their probabilities, preferably with the aid of a fancy statistical software package. Yet this scheme does not describe how actual people—including the authors of these books—reason. A professor from Columbia University was struggling over whether to accept an offer from a rival university or to stay. His colleague took him aside and said, “Just maximize your expected utility—you always write about doing this.” Exasperated, the professor responded, “Come on, this is serious.”

From economists to psychologists to John Q. Public, most people readily accept that the ideal of perfect beings with boundless knowledge and eternal time is unrealistic. Yet, they argue, without these bounds, and with more logic, we would make superior choices: we may not consider every angle, but we should. This message is not what you are going to read in the following pages.

With this book, I invite you on a journey into a largely unknown land of rationality, populated by people just like us, who are partially ignorant, whose time is limited and whose future is uncertain. This land is not one many scholars write about. They prefer to describe a land where the sun of enlightenment shines down in beams of logic and probability, whereas the land we are visiting is shrouded in a mist of dim uncertainty. In my story, what seem to be “limitations” of the mind can actually be its strengths. How the mind adapts and economizes by relying on the unconscious, on rules of thumb, and on evolved capacities is what Gut Feelings is about. The laws in the real world are puzzlingly different from those in the logical, idealized world. More information, even more thinking, is not always better, and less can be more. Ready for a glimpse?


A close friend of mine (call him Harry) once found himself with two girlfriends, both of whom he loved, desired, and admired. Two, however, were one too many. Confused by contradicting emotions and unable to make up his mind, he recalled what Benjamin Franklin had once advised a nephew in a similar situation:

April 8, 1779

If you doubt, set down all the Reasons, pro and con, in opposite Columns on a Sheet of Paper, and when you have considered them two or three Days, perform an Operation similar to that in some questions of Algebra; observe what Reasons or Motives in each Column are equal in weight, one to one, one to two, two to three, or the like, and when you have struck out from both Sides all the Equalities, you will see in which column remains the Balance. […] This kind of Moral Algebra I have often practiced in important and dubious Concerns, and tho’ it cannot be mathematically exact, I have found it extreamly useful. By the way, if you do not learn it, I apprehend you will never be married.

I am ever your affectionate Uncle,


Harry was greatly relieved that a logical formula existed to solve his conflict. So he took his time, wrote down all the important reasons he could think of, weighed them carefully, and went through the calculation. When he saw the result, something unexpected happened. An inner voice told him that it wasn’t right. And for the first time, Harry realized that his heart had already decided—against the calculation and in favor of the other girl. The calculus helped to find the solution, but not because of its logic. It brought an unconscious decision to his awareness, based on reasons obscure to him.

Thankful for the sudden solution but puzzled by the process, Harry asked himself how it was possible to make unconscious choices in contradiction to one’s deliberate reasoning. He was not the first to learn that reasoning can conflict with what we call intuition. Social psychologist Timothy Wilson and his colleagues once offered posters to two groups of women as a thank you present for participating in an experiment.2 In one group, each woman simply picked her favorite poster out of a selection of five; in a second group, each was asked to describe her reasons for liking or disliking each poster before choosing one. Interestingly, the two groups tended to take different posters home. Four weeks later, they were all asked how much they enjoyed their present. Those who had given reasons were less satisfied and regretted their choice more than those who had not given any. Here and in similar experiments, deliberate thinking about reasons seems to lead to decisions that make us less happy, just as consciously thinking about how to ride a bike or put on a spontaneous smile is not always better than its automatic version. The unconscious parts of our mind can decide without us—the conscious self—knowing its reasons, or, as in Harry’s case, without being aware that a decision has been made in the first place.

But isn’t the capability for self-reflection uniquely human and therefore uniformly beneficial? After all, doesn’t thinking about thinking define human nature? Freud used self-introspection as a therapeutic method, and decision consultants employ modern versions of Franklin’s moral algebra as a rational tool. But the evidence suggests that weighing pros and cons does not generally make us happy. In one study, people were asked about various everyday activities such as how to decide which TV programs to watch in the evening and what to buy in a department store. Did they survey all channels, using the remote control to flip back and forth through all TV stations, constantly checking for a better program? Or did they quickly stop searching and watch a good-enough program? People who reported exhaustive search in shopping and leisure were called maximizers, because they tried hard to get the best. Those who engaged in a limited search and settled quickly with the first alternative that was satisfactory or “good enough” were called satisficers.3 Satisficers were reported to be more optimistic and have higher self-esteem and life satisfaction, whereas maximizers excelled in depression, perfectionism, regret, and self-blame.


Imagine you are a contestant in a TV game show. You have outwitted all other competitors and eagerly await the $1 million question. Here it comes:

Which city has the larger population,

Detroit or Milwaukee?

Ouch, you have never been good in geography. The clock is ticking away. Except for the odd Trivial Pursuit addict, few people know the answer for sure. There is no way to logically deduce the correct answer; you have to use what you know and make your best guess. You might recall that Detroit is an industrial city, the birthplace of Motown and the American automobile industry. However, Milwaukee is also an industrial city, known for its breweries, and you might recall Ella Fitzgerald singing about her squawky cousin from there. What can you conclude from this?

Daniel Goldstein and I asked a class of American college students, and they were divided—some 40 percent voted for Milwaukee, the others for Detroit. Next we tested an equivalent class of German students. Virtually everyone gave the right answer: Detroit. One might conclude that the Germans were smarter, or at least knew more about American geography. Yet the opposite was the case. They knew very little about Detroit, and many of them had not even heard of Milwaukee. These Germans had to rely on their intuition rather than on good reasons. What is the secret of this striking intuition?

The answer is surprisingly simple. The Germans used a rule of thumb known as the recognition heuristic:4

If you recognize the name of one city but not that of the other, then infer that the recognized city has the larger population.

The American students could not use this rule of thumb because they had heard of both cities. They knew too much. Myriad facts muddled their judgment and prevented them from finding the right answer. A beneficial degree of ignorance can be valuable, although relying on name recognition is of course not foolproof. For instance, Japanese tourists will likely falsely infer that Heidelberg is larger than Bielefeld, not having heard of the latter. Nonetheless, this rule gets the answer right in most cases and does so better than a considerable amount of knowledge does.

The recognition heuristic is not only helpful for winning a million dollars. People tend to rely on it, for example, when purchasing products whose brand name they recognize. Corporations in turn exploit consumers’ heuristics, or rules of thumb, by investing in uninformative advertisement whose sole purpose is to increase brand-name recognition. The instinct to go with what you know has survival value in the natural world. Recall Dr. Seuss’s famous menu of green eggs and ham; wouldn’t you opt for the less exotic variety? By simply relying on familiar foods, you obtain the needed calories without wasting time or tempting fate by learning firsthand whether the eggs and ham are inedible or even toxic.


How does a player catch a fly ball in baseball or cricket? If you ask a professional player, he’ll likely stare blankly at you and say he’d never thought about it. A friend of mine named Phil played baseball for the local team. His coach scolded him repeatedly for being lazy, because Phil sometimes trotted over, as others did, toward the point where the ball came down. The coach thought that Phil took undue risks and insisted that he run as fast as he could in order to make any necessary last-second corrections. Phil found himself in a dilemma. When he and his teammates tried to avoid the coach’s fury by running at top speed, they missed the ball more often. What was going wrong? Phil had played as an outfielder for years and had never understood how he caught the ball. His coach, in contrast, had a theory: He believed that players intuitively calculate the ball’s trajectory, and that the best strategy is to run as fast as possible to the spot where the ball will hit the ground. How else could it work?

Phil’s coach is not the only one who thinks of computing trajectories. In The Selfish Gene, biologist Richard Dawkins writes,

When a man throws a ball high in the air and catches it again, he behaves as if he had solved a set of differential equations in predicting the trajectory of the ball. He may neither know nor care what a differential equation is, but this does not affect his skill with the ball. At some subconscious level, something functionally equivalent to the mathematical calculations is going on.5

Computing the trajectory of a ball is not a simple feat. Theoretically, balls have parabolic trajectories. In order to select the right parabola, the player’s brain would have to estimate the ball’s initial distance, initial velocity, and projection angle. Yet in the real world, balls, affected by air resistance, wind, and spin, do not fly in parabolas. Thus, the brain would further need to estimate, among other things, the speed and direction of the wind at each point of the ball’s flight in order to compute the resulting path and the point where the ball will land. All this would have to be completed within a few seconds—the time a ball is in the air. This is a standard account, according to which the mind solves a complex problem by a complex process. When it was tested experimentally, however, it turned out that players performed poorly in estimating where the ball would strike the ground.6 If they were able to estimate, one would not see them running into walls, dugouts, and over the stands trying to chase fly balls. Clearly something else is at work.


Figure 1-1: How to catch a fly ball. Players rely on unconscious rules of thumb. When a ball comes in high, a player fixates his gaze on the ball, starts running, and adjusts his speed so that the angle of gaze remains constant.

Is there a simple rule of thumb that players use to catch balls? Experimental studies have shown that experienced players in fact use several rules of thumb. One of these is the gaze heuristic, which works in situations where a ball is already high up in the air:

Fix your gaze on the ball, start running, and adjust your running speed so that the angle of gaze remains constant.

The angle of gaze is the angle between the eye and the ball, relative to the ground. A player who uses this rule does not need to measure wind, air resistance, spin, or the other causal variables. All the relevant facts are contained in one variable: the angle of gaze. Note that a player using the gaze heuristic is not able to compute the point at which the ball will land. Yet the heuristic leads the player to the landing point.

As mentioned before, the gaze heuristic works in situations where the ball is already high in the air. If this is not yet the case, the player only needs to change the last of his strategy’s three “building blocks”:7

Fix your gaze on the ball, start running, and adjust your running speed so that the image of the ball rises at a constant rate.

One can intuitively see its logic. If the player sees the ball rising from the point it was hit with accelerating speed, he’d better run backward, because the ball will hit the ground behind his present position. If, however, the ball rises with decreasing speed, he needs to run toward the ball instead. If the ball rises at a constant speed, the player is in the right position.

Now we can understand both how people catch fly balls without thinking and the cause of Phil’s dilemma. Although the coach wrongly believed that players somehow calculate a trajectory, they in fact unconsciously rely on a simple rule of thumb that dictates the speed at which a player runs. Because Phil didn’t understand why he did what he did either, he couldn’t defend himself. Not knowing the rule of thumb can have unwanted consequences.

Most fielders are blithely unaware of the gaze heuristic, despite its simplicity.8 Once the rationale underlying an intuitive feeling is made conscious, however, it can be taught. If you learn to fly an airplane, you will be instructed to use a version of this rule: When another plane approaches, and you fear collision, look at a scratch in your windshield and observe whether the other plane moves relative to that scratch. If it does not, dive away immediately. A good flight instructor will not ask anyone to calculate the trajectory of his plane in four-dimensional space (including time), estimate that of the other plane, and then see whether both trajectories intersect. Otherwise the pilot would likely not finish computing and realizing that a collision would take place before it in fact did. A simple rule is less prone to estimation or calculation error and is intuitively transparent.

The gaze heuristic and its relatives work for a class of problems that involve the interception of moving objects. In both ball games and pursuit, it helps to generate collisions, while in flying and sailing, it helps to avoid them.9 Intercepting moving objects is an important adaptive task in human history, and we easily generalize the gaze heuristic from its evolutionary origins—such as hunting—to ball games. Interception techniques travel across species. From fish to bats, many organisms have the innate ability to track an object flying through three-dimensional space, a biological precondition for the gaze heuristic. The teleost fish catches its prey by keeping a constant angle between its line of motion and that of the target, and male hoverflies intercept females in the same way for mating.10 When a dog goes after a sailing Frisbee, it is guided by the same instinct as the outfielder. In fact, a Frisbee has a more complicated flight path than a baseball; it curves in the air. By attaching a tiny camera to the head of a spaniel, a study showed that the dog ran so that the image of the ball was kept moving along a straight line.11

Interestingly, although the gaze heuristic works on an unconscious level, part of it appears in popular wisdom. For instance, when U.S. senator Russ Feingold noted that the Bush administration was clamping down on Iraq while Al-Qaeda was bubbling up elsewhere, he said: “I would ask you, Secretary Wolfowitz, are you sure we have our eye on the ball?”12 Note that the gaze heuristic does not work for all interception problems. As many ballplayers say, the hardest ball to catch is the one that heads straight at you, a situation in which this rule of thumb is of no use.

The gaze heuristic exemplifies how a complex problem that no robot could match a human in solving—catching a ball in real time—can be easily mastered. It ignores all causal information relevant to computing the ball’s trajectory and only attends to one piece of information, the angle of gaze. Its rationale is myopic, relying on incremental changes, rather than on the ideal of first computing the best solution and thereafter acting on it. Strategies relying on incremental changes also characterize how organizations decide on their yearly budgets. At the Max Planck Institute where I work, my colleagues and I make slight adjustments to last year’s budget, rather than calculating a new budget from scratch. Neither athletes nor business administrators need to know how to calculate the trajectory of the ball or the business. An intuitive “shortcut” will typically get them where they would like to be, and with a smaller chance of making grave errors.


Dan Horan always wanted to become a police officer, and even after many years in this profession it has remained his dream job. His world is Los Angeles International Airport, where he tries to spot drug couriers. Couriers fly into LAX with hundreds of thousands of dollars in cash and fly out to other American cities, delivering the drugs they’ve purchased. One summer evening in a terminal crowded with people waiting to board flights or meet incoming passengers, Officer Horan circulated among them looking for something unusual. He was wearing shorts and a polo shirt, untucked to conceal his sidearm, handcuffs, and radio. To the untrained eye, there was nothing about him that suggested he was a police officer.

A woman arriving from New York’s Kennedy Airport was neither untrained nor unwary.13 She trailed a black rolling suitcase behind her, the color that nearly everyone today prefers. She had walked only twenty feet from the jetway door when her eyes met Horan’s. In that instant, each formed an opinion about what business had brought the other to the airport, and both were right. Horan did not follow her beyond the escalator, but radioed his partner who was waiting outside the terminal. Horan and his partner were strikingly different in appearance. Horan is in his early forties and clean shaven, whereas his bearded partner was in his late fifties. Yet when the woman passed through the revolving doors into the baggage claim, it took her no longer than ten seconds to scan the crowd and recognize the partner for what he was. As the woman paced the terminal, a man who sat in a parked Ford Explorer just outside got out of the car and approached her. The woman spoke to him briefly, warning him of the detectives, then turned her back. The man returned to the car and drove off immediately, leaving her alone to face the police.

Horan’s partner approached the woman, showed his police identification, and asked for her airline ticket. She did her best to conceal her unease, smiling and chatting, yet when the detective inquired about the contents of her suitcase, she appeared insulted and would not consent to a search of her luggage. She would have to accompany him to his office, the partner said, while he attempted to get a search warrant for her luggage. Over her fierce objections, she was handcuffed, and within a few minutes, a police dog had sniffed out the traces of drugs in her suitcase. A judge agreed to a search warrant, and when the officers opened the suitcase they found about two hundred thousand dollars in cash, which the woman admitted was intended for the purchase of a load of marijuana to be shipped to New York and sold on the street.

How did Horan intuitively pick this woman out of a crowd of several hundred? When I asked him, he didn’t know. He could spot her in the large crowd, but could not spell out what seemed unusual about her. He was looking for someone who was looking for him. But what cues in her appearance made him believe that she was the courier? Horan could not say.

Although Horan’s hunches allow him to excel in his job, the legal system does not necessarily approve. American courts tend to discount police officers’ hunches, requiring them to articulate specific facts to justify a search, an interrogation, or an arrest. Even when an officer has a hunch, stops a car, finds illegal drugs or guns, and reports exactly this, judges often reject “mere hunches” as insufficient cause for a search.14 They’re trying to protect citizens from arbitrary searches and to protect their civil liberties generally. But their insistence on after-the-fact justification ignores that good expert judgment is generally of an intuitive nature. As a consequence, when police officers testify before a judge, they have learned not to use terms such as hunch or gut instinct, but to produce “objective” reasons after the fact. Otherwise, according to American law, all evidence discovered subsequent to a hunch might be suppressed, and the culprit might be acquitted.

Although many judges may condemn policemen’s hunches, they tend to trust their own intuitions. As one judge explained to me, “I don’t trust the police officers’ hunches, because they are not my hunches.” Similarly, prosecutors show little hesitation in justifying to themselves a peremptory challenge against a potential juror because she’s wearing gold jewelry and a T-shirt or does not seem too bright, given that her hobbies are eating, doing her hair, and watching Oprah. However, the issue should be neither hunches per se nor the ability to come up with reasons after the fact while hiding the unconscious nature of hunches. To avoid discrimination, the legal system instead needs to survey the quality of policemen’s hunches, that is, a detective’s actual success in spotting criminals. In other professions, successful experts are evaluated by their performance rather than by their ability to give post-hoc explanations for their performance. Chicken sexers,15 chess masters, professional baseball players, award-winning writers, and composers are typically unable to fully articulate how they do what they do. Many skills lack descriptive language.


Do gut feelings exist? The four preceding stories suggest that the answer is yes, and that both experts and laypeople rely on them. These stories are merely dots on the vast landscape of problems that intuition helps to solve: choosing partners, guessing trivia answers, catching fly balls, and detecting drug couriers. On many more occasions, intuition is the steering wheel through life. Intelligence is frequently at work without conscious thought. In fact, the cerebral cortex in which the flame of consciousness resides is packed with unconscious processes, as are the older parts of our brain. It would be erroneous to assume that intelligence is necessarily conscious and deliberate.16 A native speaker can immediately tell whether a sentence is grammatically correct or not, but few can verbalize the underlying grammatical principles. We know more than we can tell.

Let me be clear about what a gut feeling is.17 I use the terms gut feeling, intuition, or hunch interchangeably, to refer to a judgment

1. that appears quickly in consciousness,

2. whose underlying reasons we are not fully aware of, and

3. is strong enough to act upon.

But can we trust our guts? The answer to this question divides people into skeptical pessimists and passionate optimists. On the one hand, Sigmund Freud warned that it is “an illusion to expect anything from intuition,” and many contemporary psychologists attack intuition as being systematically flawed because it ignores information, violates the laws of logic, and is the source of many human disasters.18 In line with this negative spirit, our educational systems place value on everything but the art of intuition. On the other hand, ordinary people are inclined to trust their intuitions, and popular books eulogize the marvels of rapid cognition.19 In this optimistic view, people generally know what to do, albeit not why. Optimists and pessimists tend to end up agreeing that hunches are often good, except when they are bad—which is true but not very helpful. Therefore the real question is not if but when can we trust our guts? To find the answer, we must figure out how intuition actually works in the first place.

What is the rationale underlying a gut feeling? Until recently, the answer to this question was largely unknown. By definition, the person with the feeling has no idea. Prominent philosophers have argued that intuition is mysterious and inexplicable. Can science lift the secret? Or does intuition elude human grasp—God’s voice, lucky guesses, or a sixth sense beyond the limits of scientific understanding? In this book, I will argue that intuition is more than impulse and caprice; it has its own rationale. Let me first explain what I believe this rationale is not. When experiments such as the poster study demonstrated that in comparison to intuition, deliberate reasoning led to inferior outcomes, a big question mark arose: how can Franklin’s balance sheet, the holy bible of decision theory, not work? Rather than challenging the sacred authority, researchers concluded that intuition must have performed the balance sheet method automatically, attending to all information and weighing it optimally, whereas conscious thinking had not done it properly.20 Good choices must always be based on complex weighing of pros and cons, or so the conviction goes. But Franklin’s moral algebra is not my vision of intuition, and, as we will see shortly, complexity is not always best.

How do I believe gut feelings work? Their rationale consists of two components:

1. simple rules of thumb, which take advantage of

2. evolved capacities of the brain.

I use the colloquial rule of thumb synonymously with the scientific term heuristic. A rule of thumb is quite different from a balance sheet with pros and cons; it tries to hit at the most important information and ignores the rest. For the million-dollar question, we know the rationale: the recognition heuristic, whose interesting feature is that it exploits one’s partial ignorance. For catching a ball, we have identified the gaze heuristic, which ignores all information relevant to calculating a ball’s trajectory. These rules of thumb enable fast action. Each takes advantage of an evolved capacity of the brain: recognition memory and the ability to track moving objects, respectively. The term evolved does not refer to a skill made by nature or nurture alone. Rather, nature gives humans a capability, and extended practice turns it into a capacity. Without evolved capacities, the simple rule could not do the job; without the rule, the capacities alone could not solve the problem either.

There are two ways to understand the nature of gut feelings. One is derived from logical principles and assumes that intuition solves a complex problem with a complex strategy. The other involves psychological principles, which bet on simplicity and take advantage of our evolved brain. Franklin’s rule embodies the logical way: for each action, specify all consequences, weigh them carefully, and add the numbers up; then choose the one with the highest value or utility. Modern versions of this rule are known as maximizing the expected utility. This logical view assumes that minds function like calculating machines and ignores our evolved capacities, including cognitive abilities and social instincts. Yet these capacities come for free and enable fast and simple solutions for complex problems. The first goal of this book is to explicate the hidden rules of thumb underlying intuition, and the second is to understand when intuitions are likely to succeed—or fail. The intelligence of the unconscious is in knowing, without thinking, which rule is likely to work in which situation.

I have invited you on a voyage, but I must warn you: some of the insights we’ll find on our trip conflict with the dogma of rational decision making. We will encounter doubt or outright disbelief at how accurate intuition can be and suspicion of its unconscious nature. Logic and related deliberate systems have monopolized the Western philosophy of the mind for too long. Yet logic is only one of many useful tools the mind can acquire. The mind, in my view, can be seen as an adaptive toolbox with genetically, culturally, and individually created and transmitted rules of thumb. Much of what I say is still controversial. Yet there is always hope. The U.S. biologist and geologist Louis Agassiz once said about new scientific insights: “First people say it conflicts with the Bible. Next, they say it has been discovered before. Lastly, they say they have always believed it.” What I’ve written is based on my and others’ research at the Max Planck Institute for Human Development and on that of many dear colleagues all around the world.21 I hope that this little book will motivate readers to join us in exploring the new land of rationality.