Danny would later say that it was hard to explain what he and Amos were doing in the beginning: “How can you explain a conceptual fog?” he said. “We didn’t have the intellectual tools to understand what we were finding.” Were they investigating the biases or the heuristics? The errors, or the mechanisms that produced the errors? The errors enabled you to offer at least a partial description of the mechanism: The bias was the footprint of the heuristic. The biases, too, would soon have their own names, like the “recency bias” and the “vividness bias.” But in hunting for errors that they themselves had made, and then tracking them back to their source in the human mind, they had stumbled upon errors without a visible trail. What were they to make of systematic errors for which there was no apparent mechanism? “We really couldn’t think of others,” said Danny. “There seemed to be very few mechanisms.”
Just as they never tried to explain how the mind forms the models that underpinned the representativeness heuristic, they left mostly to one side the question of why human memory worked in such a way that the availability heuristic had such power to mislead us. They focused entirely on the various tricks it could play. The more complicated and lifelike the situation a person was asked to judge, they suggested, the more insidious the role of availability. What people did in many complicated real-life problems—when trying to decide if Egypt might invade Israel, say, or their husband might leave them for another woman—was to construct scenarios. The stories we make up, rooted in our memories, effectively replace probability judgments. “The production of a compelling scenario is likely to constrain future thinking,” wrote Danny and Amos. “There is much evidence showing that, once an uncertain situation has been perceived or interpreted in a particular fashion, it is quite difficult to view it in any other way.”
But these stories people told themselves were biased by the availability of the material used to construct them. “Images of the future are shaped by experience of the past,” they wrote, turning on its head Santayana’s famous lines about the importance of history: Those who cannot remember the past are condemned to repeat it. What people remember about the past, they suggested, is likely to warp their judgment of the future. “We often decide that an outcome is extremely unlikely or impossible, because we are unable to imagine any chain of events that could cause it to occur. The defect, often, is in our imagination.”?
The stories people told themselves, when the odds were either unknown or unknowable, were naturally too simple. “This tendency to consider only relatively simple scenarios,” they concluded, “may have particularly salient effects in situations of conflict. There, one’s own moods and plans are more available to one than those of the opponent. It is not easy to adopt the opponent’s view of the chessboard or of the battlefield.” The imagination appeared to be governed by rules. The rules confined people’s thinking. It’s far easier for a Jew living in Paris in 1939 to construct a story about how the German army will behave much as it had in 1919, for instance, than to invent a story in which it behaves as it did in 1941, no matter how persuasive the evidence might be that, this time, things are different.
* * *
* I owe some of this to a spectacular article about the construction and destruction of the World Trade Center towers by James Glanz and Eric Lipton, published in the New York Times Magazine a few days before the first anniversary of the attacks. William Poundstone’s book Priceless offers a more detailed account of the sway room.
? In 1986, thirty-two years after the publication of his book, Meehl wrote an essay called “Causes and Effects of My Disturbing Little Book,” in which he discussed the by then overwhelming evidence that expert judgment had its issues. “When you are pushing 90 investigations,” wrote Meehl, “predicting everything from the outcome of football games to the diagnosis of liver disease[,] and when you can hardly come up with a half dozen studies showing even a weak tendency in favor of the clinician, it is time to draw a practical conclusion. . . . Not to argue ad hominem but to explain after the fact, I think this is just one more of the numerous examples of the ubiquity and recalcitrance of irrationality in the conduct of human affairs.”
? Having realized at the start of their collaboration that they would never be able to work out who had contributed more to any given paper, they alternated lead authorship. Because Amos had won the coin flip to be lead author on “Belief in the Law of Small Numbers,” Danny was lead author on this new paper.
§ Standard deviation is a measurement of the dispersal of any population. The bigger the standard deviation, the more varied the population. A standard deviation of 2.5 inches in a world in which the average man is five foot ten means that roughly 68 percent of men are between 5 feet 7-1/2 inches and six feet 1/2 inch. If the standard deviation was zero, all men would be exactly five foot ten.
? Those lines come not from their published paper but from a summary of their work that they produced a year after the paper’s publication.
7
THE RULES OF PREDICTION
Amos liked to say that if you are asked to do anything—go to a party, give a speech, lift a finger—you should never answer right away, even if you are sure that you want to do it. Wait a day, Amos said, and you’ll be amazed how many of those invitations you would have accepted yesterday you’ll refuse after you have had a day to think it over. A corollary to his rule for dealing with demands upon his time was his approach to situations from which he wished to extract himself. A human being who finds himself stuck at some boring meeting or cocktail party often finds it difficult to invent an excuse to flee. Amos’s rule, whenever he wanted to leave any gathering, was to just get up and leave. Just start walking and you’ll be surprised how creative you will become and how fast you’ll find the words for your excuse, he said. His attitude to the clutter of daily life was of a piece with his strategy for dealing with social demands. Unless you are kicking yourself once a month for throwing something away, you are not throwing enough away, he said. Everything that didn’t seem to Amos obviously important he chucked, and thus what he saved acquired the interest of objects that have survived a pitiless culling. One unlikely survivor is a single scrap of paper with a few badly typed words on it, drawn from conversations he had with Danny in the spring of 1972 as they neared the end of their time in Eugene. For some reason Amos saved it: People predict by making up stories People predict very little and explain everything People live under uncertainty whether they like it or not People believe they can tell the future if they work hard enough People accept any explanation as long as it fits the facts The handwriting was on the wall, it was just the ink that was
invisible
People often work hard to obtain information they already have
And avoid new knowledge
Man is a deterministic device thrown into a probabilistic
Universe
In this match, surprises are expected
Everything that has already happened must have been inevitable