In the South Bronx one evening in February 1999, four plainclothes police officers drove past a young Black man standing on a front stoop. They approached him to talk, but he ran away. The young man was Amadou Diallo, a recent immigrant from Guinea with limited English who feared the plainclothesmen were local ruffians out to rob him. The police gave chase; Diallo turned and pulled something dark from his wallet. Thinking he had a gun, the officers fired on him. In moments, Diallo was dead, his wallet in his outstretched hand. Shocked by their mistake, one of the officers “sat down on the steps, next to Diallo’s bullet-ridden body, and started to cry” (336). The officers were charged with first-degree manslaughter and second-degree murder.

The story illustrates how, in encounters with others, people make continuous, rapid-fire judgments, inferring and predicting their state of mind. Subtle facial expressions reveal intent; recognizing them involves thin-slicing. These impressions “just come to you, blink” (337). With Diallo, the officers made three crucial mistakes. They assumed a man out for some air was suspicious, they backed up and found him still there instead of running away, but they ignored this fact, and they overreacted to Diallo reaching into his pocket. His death was due to a failure of the kind of mind reading people do all the time. The jury found the officers not guilty, but many people believed them guilty of racism, and protests broke out.

As he considers how “mind reading” works, Gladwell turns to psychology professor Silvan Tomkins, who had an uncanny ability to read faces. His student, Paul Ekman, proved that human facial expressions are universal, not culturally determined; Ekman also catalogued 3,000 individual expressions in the Facial Action Coding System (FACS). He discovered that people who copy a given facial expression undergo the same emotions and physiological responses as people who simply recall and relive those feelings.

People can’t completely hide automatic micro-expressions; these aren’t under conscious control and are detectable by observers to ascertain a person’s true feelings. If people could shut off those expressions, their ability to communicate would become severely limited—parents would be unable to know what their babies are feeling, couples would cease to be intimate, and so on.

Instead, people have a natural ability to read faces. That being the case, Gladwell questions how the police so badly misread Amadou Diallo. It seems like it would have been obvious: “Diallo was innocent, curious, and terrified—and every one of those emotions must have been written all over his face. Yet they saw none of it” (371).

To make sense of this, Gladwell notes that in normal conversation, people watch each other’s faces, especially the eyes, for cues to the other person’s thoughts and feelings. Those with autism are often unable to do this; they are “mind-blind” and must focus entirely on spoken words to glean anything from an interaction. For example, “Peter”—an intelligent, independent man with both graduate degrees and an autism diagnosis—watched the film Who’s Afraid of Virginia Woolf?, about an intense and difficult encounter between four people. Cameras monitored Peter’s eye movements; most viewers spend a great deal of time observing the actors’ faces and eyes, but Peter did little of this. Human brains have a specific area—the fusiform gyrus—that recognizes faces; they use another, weaker area—the inferior temporal gyrus—to recognize objects. People with autism use the weaker area to deal with faces, as if faces were things, like chairs or hammers.

Gladwell argues that in stressful situations, any person may use their brain as people with autism do. Extreme arousal can make people mind-blind; they can no longer appropriately interpret other people’s faces and gestures. Police officers involved in shootings commonly report “extreme visual clarity, tunnel vision, diminished sound, and the sense that time is slowing down” (390). Heart rates are around 115 to 145 beats per minute; above that rate, motor skills and mental functions begin to break down, and actions become uncoordinated and inappropriately aggressive. Major urban riots have begun when police, chasing a suspect at high speed, become overly excited and beat up or kill the suspect.

Moreover, in emergencies, there’s often little or no time to react thoughtfully, and the mind defaults to old biases and stereotypes. Two-officer teams get into more trouble than single officers do because two may rush forward with aggressive bravado where a solo officer would take a cautious moment to evaluate the situation.

With practice, however, emergency responders can learn not to panic. Gavin de Becker’s private security company trains its bodyguards—using painful plastic marking capsules fired at them—to stay calm and in control even when hit by hostile fire. People can also learn to decipher micro-expressions, which improves mind reading. Ekman’s law enforcement seminars teach students in 35 minutes to correctly read a large group of tiny facial expressions. With such awareness, responders have more ways to read a situation and make better decisions. Gladwell concludes that Diallo died because the police, two of them new to the force and the neighborhood, became overly excited and, in a panic, catastrophically misread the situation.

Abbie Conant played trombone. In 1980, she auditioned behind a curtain for a position in the Munich Philharmonic, and the judges immediately wanted her; they sent home the other applicants. Then they discovered that she was a woman, playing what they considered a man’s instrument. Though they admitted her to the orchestra, they tried in several ways to make her leave—demoting her, paying her less, and the like. She took them to court and won, largely because the conductor originally cried, “That’s who we want!” (443) when they first heard her play.

Orchestras are traditionally composed almost entirely of men, and music directors often believe women are weaker players. In recent decades, musicians have demanded more fairness, and audition candidates have started performing while hidden behind screens. The result is that orchestras have increased the number of women players fivefold. The practice also benefits musicians who appear belabored, nerdy, or unconfident but produce excellent sound. Even the particular instrument they perform—its materials or manufacturer—can cause bias. It’s been said that, “There is only one way to make a proper snap judgment […] and that’s from behind a screen” (439).

This practice underscores that rapid cognition can be improved, and biases avoided, by making small changes to the settings in which intuitive judgments take place. Much as orchestras put player candidates behind screens; Thomas Hoving, former director of the Metropolitan Museum of Art, has works of art appear suddenly—surprising him in a closet or from under a black cloth pulled away quickly—so that his first impression is stripped of pre-judgment. These small tweaks clear away the biases that cling to first impressions so that the true nature of the situation can shine through in an instant.

During the American Civil War, Union general Joe Hooker faced Robert E. Lee’s forces at Chancellorsville. Hooker had twice as many soldiers and more cannons than Lee and managed to sneak half his force behind Lee’s position. Instead of retreating into the waiting jaws of the rear guard, Lee’s men attacked to the front, stunning Hooker, and then attacked him at his strongest point when those troops were eating dinner, causing them to flee in a rout. The episode demonstrates that war isn’t an arithmetic problem; it’s an activity that requires an ineffable quality of judgment. Lee, finding himself pressed from both front and behind, realized that Hooker’s forces were halved, so he attacked their front troops with his own comparable force and, using superior tactics, won the day.

The story also underscores that instinct is fragile and easy to disrupt. The northern general, with his network of spies and observation balloons, knew much more than Lee about the disposition of forces, but sometimes too much information is thwarted by not enough information. Lee used counterintuitive tactics that interrupt Hooker’s flow of intuition, and Hooker—already intimidated by Lee’s reputation—simply caved in. Similarly, the US military, inundated in 1941 with information about Japanese forces, was surprised when the Asian nation bombed Pearl Harbor. Meanwhile, American journalists, with much less information, figured out the likely attack beforehand. At Chancellorsville, Pearl Harbor, and the Millennium Challenge, the losers had much more information than the winners did. What counts isn’t knowledge, Gladwell reiterates, but wisdom.

Gladwell returns to the question of bias, noting that Black men are incarcerated for drug crimes at much higher rates than white men. He suggests that putting screens in the courtroom or placing the accused in a separate room to communicate by text might reduce the effects of unconscious bias during trials.

Overall, Gladwell argues, research suggests that when choices involve few bits of information, people choose better by thinking it through, but when faced with large amounts of information, they fare better by going with their gut.