The Israeli intelligence service asked the great psychologist Daniel Kahneman for help in the 1970s, and Kahneman came back with a suggestion: Get rid of the classic intelligence report. It allows leaders to justify any conclusion they want, Kahneman said. In its place, he suggested giving the leaders estimated probabilities of events.

The intelligence service did so, and an early report concluded that one scenario would increase the chance of full-scale war with Syria by 10 percent. Seeing the number, a top official was relieved. “Ten percent increase?” he said. “That is a small difference.”

Kahneman was horrified (as Michael Lewis recounts in his book “The Undoing Project”). A 10 percent increase in the chance of catastrophic war was serious. Yet the official decided that 10 wasn’t so different from zero.

Looking back years later, Kahneman said: “No one ever made a decision because of a number. They need a story.”