The Undoing Project: A Friendship That Changed Our Minds

Though Danny and Amos had been at the University of Michigan at the same time, their paths did not cross until they were both working at Hebrew University. Amos came into Danny’s class and guest lectured on some of the research led by Ward Edwards at his lab at the University of Michigan. Edwards was testing a theory on whether people more or less acted as if they knew Bayes’s theorem, a formula that calculated probabilities and odds when people were given new information, such as pulling either a red or white poker chip out of a bag. After completing a math textbook called Foundations of Measurement, Amos was looking for a new line of inquiry. As he explained Edwards’s research in Danny’s class, the students in the room were surprised. Even though Danny and Amos had already established themselves as the stars of the psychology department, the two had never interacted until that guest lecture.

The moment proved to be underwhelming. Danny was astounded by how unimpressive Edwards’s research was, including the premise that anchored the work. As Lewis writes, “to Danny, the experiment that Amos described sounded incredibly stupid. After a person has pulled a red chip out of a bag, he is more likely than before to think the bag to be the one whose chips are mostly red: Well, duh” (147). Amos’s summary of the research on whether people were “conservative Bayesians,” or intuitive statisticians, was altogether disappointing for Danny. Amos left Danny’s lecture hall changed, mired “in a state of mind unusual for him: doubt” (151).

This initial meeting between Danny and Amos, underwhelming as it was, served to provide a “collision” between the two top minds at Hebrew University, and from then they became almost inseparable, as if brought together by fate. As Lewis explains, “The students who once wondered why the two […] kept their distance from each other now wondered how two so radically different personalities could find common ground, much less become soul mates” (154). During their waking hours, Danny and Amos were usually together, arguing behind closed doors in both English and Hebrew. Two brilliant minds were now working in tandem, and this initial momentum turned into their first paper, “Belief in the Law of Small Numbers,” which pointed out that most statisticians did not use a large enough sample size when making inferences, and that these inferences could therefore be misleading. This was just the beginning of their joint efforts.