In 1971, Daniel Kahneman and Amos Tversky, psychology professors at the Hebrew University of Jerusalem at the time, began a sabbatical year at the Oregon Research Institute. The two Israelis, both in their 30s, seemed like a study in contrasts; where Tversky, a decorated paratrooper with shrapnel lodged in his body, was optimistic and analytical, Kahneman was pessimistic and intuitive. But they shared a sense of humor, and an interest in the psychology of mistakes.
That year they ran dozens of experiments. In one, they built a wheel marked 0 to 100, but rigged it to stop on only 10 or 65. After each spin, the subject wrote down the number and was then asked to guess the percentage of countries in the United Nations that are African. On average, those who spun a 10 guessed 25 percent, while those who spun a 65 guessed 45 percent.