The Undoing Project

Michael Lewis’s The Undoing Project is more than a biography—it’s a story about friendship, intellect, and how two men changed our understanding of the human mind. The book follows Daniel Kahneman and Amos Tversky, two Israeli psychologists who challenged the world’s assumptions about rationality. Together, they revealed that our decisions are not driven by logic and statistics, but by emotion, habit, and the subtle biases hidden in our thinking.

The two men came from dramatically different backgrounds. Kahneman, born in Tel Aviv in 1934, spent his childhood in Nazi-occupied France, constantly on the run with his family. The fear and uncertainty of those years left him deeply reflective and observant of human behavior. He became fascinated by the question of why people make bad judgments even when they have good intentions. After immigrating to Israel in 1946, he studied psychology at Hebrew University, where he began exploring how perception and intuition influence behavior.

Amos Tversky, born in Haifa in 1937, was almost Kahneman’s mirror image. Where Kahneman was self-doubting and reserved, Tversky was bold, confident, and endlessly curious. A paratrooper in the Israeli army, he once dove on a live grenade to save his unit—only to discover it was a dud. That fearlessness defined his approach to life and research. He combined a mathematician’s precision with a poet’s love of paradox, constantly looking for the elegant logic behind human mistakes.

When the two met at Hebrew University in the late 1960s, they were both teaching psychology but approached it differently. Kahneman studied how perception fooled the senses; Tversky studied how logic failed the mind. Their first conversation turned into an argument about human reasoning that lasted hours—and marked the beginning of a collaboration that would last decades. They spent endless days locked in their offices, arguing, laughing, and building theories that would redefine how the world understood decision-making. Their partnership was so close that colleagues joked, “They share a single mind in two bodies.”

The Myth of the Rational Mind

Before Kahneman and Tversky’s work, the dominant model in economics and psychology was that humans are rational actors who make decisions by weighing risks and rewards logically. This was the foundation of expected utility theory, a principle dating back to the 18th century. People were assumed to maximize benefit and minimize loss through careful calculation.

Kahneman and Tversky dismantled this assumption. Through hundreds of clever experiments, they proved that the human brain often substitutes intuition for logic, creating systematic, predictable errors. Their work exposed the gap between how we think we think and how we actually think.

They discovered that we use heuristics—mental shortcuts—to make complex judgments quickly. These shortcuts are efficient but flawed, leading to biases that distort perception and reasoning. What made their research so radical was not just the identification of these errors, but the discovery that they occur consistently across people, professions, and cultures. Bias wasn’t random—it was universal.

The Representativeness Heuristic: Mistaking Stereotypes for Truth

The first major heuristic they uncovered was representativeness—our tendency to judge probabilities based on resemblance rather than logic.

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