It’s no accident that Oprah Winfrey’s latest best seller is called “What I Know For Sure,” rather than “Some Things That Might Be True.”But as Christopher Chabris and Daniel Simons point out in the Times, when it comes to memory this is not true. Many studies have shown that in some circumstances the more certain people feel about what they remember, the less likely it is to be true. One of the main recommendations psychologists have about police line-ups is that the police must take note of how confident the witness feels at the time of making the identification. Because months later, after the witness has thought it over more and more, the memory of the face in the line-up completely replaces whatever memory there was from the scene of the crime, and many witnesses have claimed complete certainty in court about identifications that were very tentative when they were first made. One thing we know about memory is that it does not get better with time, so this is nonsense. But jurors are much more likely to be persuaded by a witness who claims to be certain than one who admits to uncertainty.
I would extend this to many other areas of life. When scientists leap to bold conclusions from single experiments, I shake my head. When politicians claim to be completely certain that their policies will improve the economy, I shrink back, because I do not think we have the sort of economic knowledge that such certainty would require. (This is why I don't admire Paul Krugman as much as my liberal friends seem to.) As Voltaire said, “Doubt is not a pleasant condition, but certainty is an absurd one.”