The definition of morality is highly "idiosyncratic," Dunning says. We tend to see things as moral if they are the kind of things we do. If we give to charity, then giving is a moral obligation. Likewise if we consider ourselves honest, or loyal, or altruistic, or religious.
Our sense of morality, then, becomes an expression of ourselves.
But that doesn't explain why we seem to think we're so much better, so much "holier," than we really are.
Dunning says one reason our egos are inflated is we get a lot of positive feedback from our peers. Even if some people think you're "a jerk," he says, they aren't likely to say that to your face.
Instead, we're often told how neat we are, at least by our friends, so we tend to believe we are doing the right things. We're nice people, after all.
So our moral judgments become a self-fulfilling prophecy. If it's the kind of thing we do, it must be moral, or we wouldn't be doing it.
"We define morality by looking at our own behavior," Epley says.
But does believing that we are moral really have any effect on how we live?
Dunning thinks it probably does.
Living Up to Standards
"Once you say you are a moral, wonderful, generous person, you have to live up to those standards," Dunning says. "So even if you have overestimated yourself, you are constrained" by your self image, he adds.
Living in a world with people like that is preferable to living "in a world where people basically say they are selfish jerks," Dunning says, "because then they would be constrained to act like selfish jerks."
But there is a down side to all this self anointed sense of morality, he adds.
"If people think they are morally superior to others, they are going to be too harsh in judging other people," he says.
"They don't realize that in the same situation, they are going to act the same way."
Lee Dye’s column appears weekly on ABCNEWS.com. A former science writer for the Los Angeles Times, he now lives in Juneau, Alaska.