And yet, Sandusky continues to insist that he is innocent.

"They could take away my life, they could make me out as a monster, they could treat me as a monster, but they can't take away my heart," he said in a recorded statement. "In my heart, I know I did not do these alleged disgusting acts. My wife has been my only sexual partner and that was after marriage. Our love continues."

Despite overwhelming evidence and testimony against him, Sandusky appears to truly believe he did nothing wrong.

How can he possibly be so completely delusional?

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Sandusky's faith in his own lies is, in fact, an extremely common and very human trait, experts say. And even though his denial led him to commit destructive and terrible acts far worse than what most people would ever do, his ability to distort and then reinforce his own sense of the truth illustrates the extreme flexibility of the human mind to alter memories.

"Self-deception can become deeply entrenched if it's something we practice and continue to practice and continue to continue to practice," said Robert Trivers, an evolutionary biologist at Rutgers University and author of "The Folly of Fools: The Logic of Deceit and Self-Deception in Human Life."

"You deny the facts, then you deny that you deny them, then new evidence comes in and you deny that," he added. "To get Sandusky into the state of mind we see him in at the present requires that he had been engaging in this kind of denial and self-deception for years and years and years as part of making this behavior acceptable to himself and even admirable, since he thought he was setting the foundation to aid children."

Just about all of us deceive ourselves to some degree. Studies show, for example, that most people rate themselves as higher than average on scales of attractiveness, intelligence, generosity and other measures of appeal to others.

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In many ways, these kinds of mild delusions can be a good thing, providing a confidence boost that improves our lives. Whether it's about the size of a pimple or the likelihood of succeeding at opening a new restaurant, little lies can lead to success.

From an evolutionary standpoint, Ariely said, learning to believe our own lies can boost our chances of survival, helping us take risks and gamble in uncertain situations.

"Ask yourself whether you would always want to know the truth about yourself. Ask yourself whether you want your husband to always tell the truth," said Dan Ariely, a psychologist and behavioral economist at Duke University, and author of "The Honest Truth About Dishonesty: How We Lie to Everyone--Especially Ourselves."

There are lots of benefits to seeing ourselves as better than we are."

It can also work the other way: On a daily basis, we delude ourselves about the safety of getting in our cars, believing that we're in control and unlikely to die. Likewise, many people think they're less likely to succumb to a heart attack than they really are, and those beliefs fuel bad choices.

In one study, Ariely and colleagues gave two groups of people an SAT-like test and told them that they would be paid for each correct answer. One group received versions of the test with answers at the bottom, though they were told not to peek until after they had finished. The other group had no choice but to do the work on their own.

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When given the option, the researchers found, lots of test-takers cheated by looking at the answers before they were done -- leading the group that was given answers to score consistently better than the group that received only the questions.

But that's not all. Many of the cheaters actually came to believe that they were as good as their deceptive scores would indicate.

In subsequent tests that did not provide answers, the cheating group predicted they would do as well as they had the first time around, and they ended up losing money on that bet. People who received a certificate proclaiming the scores they had earned through cheating were even more convinced about their superior skills.

Results like these illustrate how people so end up lying on their resumes, Ariely said. As exaggerations accumulate on an official document, those lies begin to reinforce false memories.

For many people, one small lie often leads to another, and that's where trouble begins, especially when combined with dangerous desires.

"If someone has a strong motivation toward something, they can use their cognitive flexibility, memory and reasoning to basically tell themselves a story where they've really misbehaved and the still think of themselves as good people," Ariely said. "I think this is most likely a much more common thing than we think."

"When you and I look at dishonest acts, we see where people ended up and we say to ourselves we could never have done that," he added. "In all the cases of big cheaters I've talked to, they thought about one small step and another small step. In this way, they got themselves into a very different kind of situation."