The Undoing Project

Human beings make terrible decisions. This is not a philosophical position. It's a scientific fact, backed by decades of research. We hire the wrong people, invest in the wrong stocks, diagnose the wrong diseases, and send the wrong soldiers into battle. We trust our gut feelings precisely when those feelings lead us astray. And we do it again and again, in patterns so predictable that psychologists can name them.

Michael Lewis knows this problem well. In 2003, he wrote Moneyball, the story of how the Oakland Athletics transformed baseball by ignoring what scouts saw with their eyes and trusting instead what the data revealed. The scouts had decades of experience. They knew talent when they saw it. But they were wrong, systematically wrong, and the numbers proved it. The book became a sensation, a parable about the triumph of algorithms over intuition.

But Moneyball left a question hanging. If human judgment is so flawed in baseball, what about everywhere else? What about medicine, where doctors misdiagnose patients based on first impressions? What about investing, where experts buy high and sell low? What about warfare, where generals repeat the mistakes of their predecessors?

The Undoing Project is Lewis's attempt to answer that question. It is, as he explains in the introduction, a thematic sequel to Moneyball. But instead of telling the story of a baseball team that learned to trust data, it tells the story of two psychologists who spent their lives trying to understand why human intuition goes wrong in the first place. As Lewis writes, "the enthusiasm for replacing old-school expertise with new-school data analysis was often shallow." You cannot simply swap intuition for algorithms. You have to understand what the mind is doing when it makes a mistake. And that understanding came from two men who were, in every way that matters, opposites.

Daniel Kahneman was an outsider. A Holocaust survivor who spent his childhood in hiding, he grew up anxious, insecure, and convinced that he was wrong about everything. He became a psychologist because he wanted to understand his own mind, which felt to him like a mystery he could never solve. When he worked for the Israeli military, he discovered something remarkable: when he removed his own gut feelings from his predictions, those predictions became more accurate. His intuition was not a gift. It was an obstacle.

Amos Tversky was the opposite. He was an insider, a decorated paratrooper who had jumped out of airplanes and led men into battle. He was magnetic, confident, and certain he was right. At parties, he was the center of attention. In academic debates, he was the one people remembered. He approached intellectual life the way he approached war: strategically, aggressively, with an eye for the weak point in the enemy's defenses. He was, in every way, the person Kahneman was not.

Together, they would change how we think about thinking.

Their collaboration began in the late 1960s at Hebrew University in Jerusalem. At the time, psychology was dominated by the idea that people were essentially rational. Given enough information, they would make logical decisions. Kahneman and Tversky suspected this was wrong. They ran experiments, conducted thought exercises, and published papers that showed, over and over, that the human mind is not a rational calculator. It is a machine for telling stories, and those stories are often wrong.

They called the mental shortcuts people use "heuristics." They called the systematic errors those shortcuts produce "biases." And they showed that these errors were not random. They were predictable. Given the same situation, most people would make the same mistake. The mind had rules, and those rules could be learned, tested, and even overturned.

What drove them was not just intellectual curiosity. It was patriotism. Both men were Israeli, and Israel in the 1960s and 1970s was a country under constant threat. Wars could break out at any moment. Intelligence failures could cost thousands of lives. Kahneman and Tversky believed that if they could understand how people made decisions under uncertainty, they could help their country make better ones. They were not interested in abstract theory. They wanted to be useful.

And they were. Their work on heuristics and biases would eventually transform fields far beyond psychology. Economists began to realize that their models of rational behavior were built on false assumptions. Doctors began to recognize that their diagnoses were influenced by irrelevant factors. Investors began to see that their confidence in a stock was inversely related to their actual ability to predict its performance.

But the story of The Undoing Project is not just about ideas. It is about a friendship. Kahneman and Tversky worked together for more than a decade, and their collaboration was so intense that they often could not tell where one person's thoughts ended and the other's began. They were, as Lewis describes them, "soul mates." But like many soul mates, they eventually fell apart. Their undoing was caused by the very thing they studied: human judgment, flawed and irrational, even in those who understood it best.

Lewis begins the book with a story from the world of professional basketball. Darryl Morey, the general manager of the Houston Rockets, was hired because the team's owner wanted "a Moneyball type." Morey was not a former player or coach. He was an analyst who believed that algorithms could outperform human intuition. And he was right. Under his leadership, the Rockets became one of the most successful teams in the NBA. But he also made mistakes. The most famous was passing on Marc Gasol, a player the Rockets had internally nicknamed "Man Boobs." The algorithm said Gasol would be great. The scouts looked at him and saw a slow, overweight European. The scouts won. Gasol became a three-time All-Star. The Rockets lost.

This is the problem that never goes away. We know that our minds are flawed. We know that data is more reliable than intuition. And yet we still trust our guts. We still listen to the experts who tell us stories. We still make the same mistakes, generation after generation.

Kahneman and Tversky spent their lives trying to understand why. They never fully succeeded. But what they discovered changed the world. And the story of how they discovered it is, in the end, a story about two people who found in each other a partner for the most important conversation of their lives.

What happens when the people who understand human error best cannot save their own relationship? What does it mean when the experts on decision-making make the worst decision of all?