In 1969, the psychologist Robert Zajonc published an article about a curious study. He'd posted a silly-sounding word—either kardirga, saricik, biwonjni, nansoma, or iktitaf—on the front page of some student newspapers in Michigan every day for several weeks. Then he sent questionnaires to the papers' readers, asking them to guess whether each word referred to "something 'good' " or "something 'bad.’ " Their answers were consistent, if a little strange: Nonsense words that showed up in print many times were judged to be more positive than those that appeared just once or twice. The fact of their repetition, said Zajonc, gave the words an aura of warmth and trustworthiness. He called this the mere exposure effect.
Maybe you've heard about this study before. Maybe you know a bit about Zajonc and his work. That's good. If you've already seen the phrase mere exposure effect in print, then you'll be more likely to believe that it's true. That's the whole point.
Psychologists have devised other ways to make a message more persuasive. "You should first maximize legibility," says Daniel Kahneman, who describes the Zajonc experiment in Thinking, Fast and Slow, a compendium of his thought and work. Faced with two false statements, side-by-side, he explains, readers are more likely to believe the one that's typed out in boldface. More advice: "Do not use complex language where simpler language will do," and "in addition to making your message simple, try to make it memorable." These factors combine to produce a feeling of "cognitive ease" that lulls our vigilant, more rational selves into a stupor. It's an old story, and one that's been told many times before. It even has a name: Psychologists call it the illusion of truth.
See how it works? A simple or repeated phrase, printed in bold or italics, makes us feel good; it just seems right. For Kahneman, that's exactly what makes it so dangerous. He's been working on this problem since 1969, when he met his late collaborator, Amos Tversky, at the Hebrew University in Jerusalem. Their famous project, for which Kahneman won a Nobel Prize in 2002, was to illuminate and categorize the pitfalls of intuition, and show that the "rational actor" of economic theory was a fiction. We're all subject to a set of reliable biases and illusions, they argued; our decisions are consistently inconsistent. For their first major paper, published in Science in 1974 and reprinted in the appendix of Thinking, Fast and Slow, Kahneman and Tversky sorted through the foibles of human judgment and laid out a menu of our most common mistakes. Here was a primer on how perceptions go wrong and a guide for their diagnosis.
The Science paper ticked off some 20 effects and biases, many reduced to simple phrases and set off in italics to make them easier to follow. Thinking, Fast and Slow updates this list with another four decades of work in the field, amounting to a Diagnostic and Statistical Manual of Mental Disorders for the irrational mind. In the course of 418 pages, Kahneman designates no fewer than three biases (confirmation, hindsight, outcome), 12 effects (halo, framing, Florida, Lady Macbeth, etc.), four fallacies (sunk-cost, narrative, planning, conjunction), six illusions (focusing, control, Moses, validity, skill, truth), two neglects (denominator, duration) and three heuristics (mood, affect, availability). A new characterization of how we misjudge the world—and a new catchphrase that we might use to describe it—appears in almost every chapter of the book. That's Kahneman's goal: He's trying to give us "a richer language" for talking about decisions, he says, and "a precise vocabulary" for their analysis.
It's a promising thought, but to place this book in the rubric of self-help would be to mistake Kahneman—who lived for several years in Nazi-occupied France—for a benighted optimist. Again and again he reminds us that having the means to describe your own bias won't do much to help you overcome it. If we want to enforce rational behavior in society, he argues, then we all need to cooperate. Since it's easier to recognize someone else's errors than our own, we should all be harassing our friends about their poor judgments and making fun of their mistakes. Kahneman thinks we'd be better off in a society of inveterate nags who spout off at the water-cooler like overzealous subscribers to Psychology Today. Each chapter of the book closes with a series of quotes—many suggested by the author's daughter—that are supposed to help kick off these enriching conversations: You might snipe to a colleague, for example, that "All she is going by is the halo effect"; or maybe you'd interrupt a meeting to cry out, "Nice example of the affect heuristic," or "Let's not follow the law of small numbers."