Given the track record of such things, predictions of the world's end are best ignored. But still I think we should we pay attention to Harold Camping, the influential 89-year-old evangelist who says Jesus will return on May 21. It's not that Camping is right. Indeed, I will be so bold as to claim that a 2,000-year-old Jew -- Jesus or any other -- will not descend from the clouds on May 21. But something important probably will happen on May 22: a demonstration that people strongly committed to the truth of a proposition are capable of dismissing even overwhelming evidence that they are wrong. Please note that I said "people." Not "religious zealots." Not "cranks." Just "people." The ability to evade evidence and keeping believing even when it's bonkers to do so is universal. We all possess it. And if we're not careful we will exercise it, and fool ourselves badly. We know this thanks in large part to the work of the legendary psychologist Leon Festinger. "Suppose an individual believes something with his whole heart," Festinger and colleagues Henry Riecken and Stanley Schachter wrote more than half a century ago. "Suppose further that he has a commitment to this belief, that he has taken irrevocable actions because of it; finally, suppose that he is presented with evidence, unequivocal and undeniable evidence, that his belief is wrong; what will happen? The individual will frequently emerge, not only unshaken, but even more convinced of the truth of his beliefs than ever before." This wasn't conjecture. It was observation. Prophecies routinely fail. Just as routinely, believers insist they didn't. A famous example is the New England farmer William Miller, whose Bible study convinced him the world would end "about the year 1843." When the year drew near, the "Millerite" movement fixed a precise date for the end of the world. Excitement built. The day dawned. Nothing happened. Disappointed, the Millerites went back to the Bible. And lo! They discovered that the correct date was still to come! They became even more certain and excited than before. But that date also came and went. So the process was repeated. And repeated. Only after the world had failed to end four times did the Millerites finally give up. Festinger and his colleagues witnessed this process first-hand in 1954, when they infiltrated a small apocalyptic sect. The group believed that on Dec. 21, at midnight, they would be whisked off the planet shortly before a terrible cataclysm destroyed the world as we knew. Midnight came. Nothing happened. What now? As the psychologists expected, reactions differed. Those with only a modest commitment to the prophecy quietly drifted away. But other group members had quit jobs, sold possessions, and cut ties with loved ones. They agonized for hours. How could they have been wrong? Impossible. There must be some explanation. Suddenly, the leader had a revelation: The prophecy hadn't failed! God had been so moved by the faith of the little group that He had decided to spare the world! Joy and jubilation followed -and everyone became even more convinced they had been right all along. Obviously, these are extreme cases. But for Festinger, they were merely dramatic illustrations of a basic feature of human psychology. He called his theory "cognitive dissonance." When two thoughts sit uncomfortably together -"I gave up everything because it's the end of the world" alongside "the world's still here" -we seek to reconcile them. By ignoring. By forgetting. By rationalizing. Somehow or other, whatever it takes. Festinger's theory is now well supported by decades of research. Two key points emerge. One, cognitive dissonance is ubiquitous. We all deal with it every day, almost always without realizing it. Say you finally go to that fancy restaurant, spend a fortune on a meal, and the food you get just isn't that good. What happens next? You can't reduce the bill. But you can elevate your opinion of the meal. And you probably will, without knowing you did, or why. The second insight is that when commitment is intense, cognitive dissonance can make it all but impossible to say "I was wrong." Consider the case of John DeWitt, the American general in charge of security on the Pacific coast after the attack on Pearl Harbor. DeWitt was certain Japanese-Americans would unleash a wave of sabotage, so he called for them to be interned. Two years passed. There was no sabotage. None. Any chance DeWitt had been wrong? Of course not. "The very fact that no sabotage has taken place is a disturbing and confirming indication that such action will be taken," he said. We see this all the time in politics. In the late 1980s, after inflation had fallen dramatically in the United States, surveys found that most Democrats believed inflation was still high. Why? Because the president was Republican. Distorting the facts eased the cognitive dissonance of a major improvement happening under a president they considered a major disaster. (And no, it's not a liberal flaw. In 1996, after the deficit had been slashed under a Democratic president, more than half of Republicans believed the deficit was bigger.) So what about old Harold Camping? Will he shrug and say "I guess I was wrong" when Jesus fails to make an appearance May 21? I'd bet a week's pay he won't. Instead, he will go back to his Bible study, do some math, and discover that the real date is some time in the future. How can I be so sure? Because Camping used to preach that the world would end on Sept. 6, 1994. He wasn't wrong then. He won't be wrong now. True Believers never are.