Kahneman and Tversky Discover that Information Persuades Nobody

Shortly before he died in 1996, Professor Amos Tversky ran an experiment alongside Lyle Brenner and Derek Koehler at Stanford University. And it confirmed everything he'd learnt about human decision making.  

It was kind of a mock trial where a union organiser has been arrested for trespassing at a pharmacy. It later become clear that he had done nothing wrong. What the experimenters found was, if the story was told well enough, if it was coherent enough, it didn’t matter when a key piece of information shows someone’s innocence or guilt. What matters is the shape of the story. That’s what lingers in people’s minds. 

Professor Tversky had learnt something similar when he worked with Daniel Kahneman in the 1970s. We’re not nearly as rational as we like to believe. Marketers are kidding themselves if they think a single proposition will persuade a customer. Lawyers are crazy if they think a “smoking gun” will alone persuade a jury. And data won’t change the mind of even the most proudly rationalist policy maker.

Of course Kahneman and Tversky new something about the power of story from their own lives. They were both grandsons of Rabbis - those teachers of the world’s most famous and most enduring stories. And, in 1973, they both fought in a war where all the data showed their side should have lost - the Yom Kippur War of 1973. 

But the power of story over data was something that became clear later. In 1975, Israel’s Foreign Minister, Yigal Allon, asked Kahneman to do some research on the likelihood of war with Syria. His paper, which he wrote with the head of Israel’s intelligence unit, Zvi Lanir, held what should have been shocking information about the dangers of upsetting Syria. They found that certain moves Israel made in its dealings with Syria could increase the likelihood of war with Syria by 10%.

But when Kahneman and Lanir presented their data to Israel’s Foreign Minister, Yigal Allon, he sniffed at it. The numbers meant nothing. Minister Allon preferred to trust his instincts. As Daniel Kahneman revealed in an interview with Vanity Fair, this was his epiphany on persuasion. “That was the moment I gave up on decision analysis. No one ever made a decision because of a number. They need a story.” 

Or, as Kahneman explained in The Scientific American, “[we] build the best possible story form the information available… and if it is a good story, [we] believe it.” 

Robert MacNamara, the brilliant US Secretary of Defense may have been right. You shouldn’t make a decision until you “Get the data”. However you should never expect that data to persuade the people. 

Stories change minds. Not information. Not propositions. And certainly not data.