As former CIA director David Petraeus gets his first taste of unemployment this week, he will have plenty of time for reflection. Finding himself in the center of a whirlwind of gossip, conspiracy, and innuendo, it will be impossible for him to gain much perspective on the wreckage of his career. Like the pundits, he may be asking himself: Where did I go wrong? I would like to propose a perhaps counterintuitive answer: Petraeus went wrong by never going wrong.

"He sees this as a failure, and this is a man who has never failed at anything," CNN quoted a friend of Petraeus's saying about the former general.

He never failed at anything?

If you have never failed at anything, then you haven't been trying hard enough, aren't very imaginative, or have had such extraordinarily good luck that you have come to believe you are invincible. And that, of course, is the problem.

"Success confers its own blindness," Emily Brown told me. She's a marriage counselor who has worked extensively with couples who have had the experience of infidelity.

"Successful people believe they can get away with it," she says. "I talked once to a group of men who'd all become millionaires before the age of 40, and they'd had affairs. They don't even see the danger! It isn't a love of risk. They think: The wives will never know, so where's the harm? Everything else in their lives has worked out, so they think they have some kind of magic, that their success has meant that they can have everything they want and they're invulnerable. And they were completely blind to the harm they had done."

Most of us make mistakes, and we should take some comfort in the fact that these usually remind us that we are fallible. If we are very lucky, we make mistakes from which we can learn and recover. Most of us have the oddly good luck not to imagine that we are infallible.

I'm a big believer in mistakes. Not just because I make lots of them--like everyone, I try very hard not to--but because every mistake contains learning. The best mistakes are the ones from which you learn the most and that you never forget. I would bet Petraeus thought that never failing was a sign of his genius. The truth is probably that he made mistakes, but he didn't take time to learn from them. Or, hauntingly, he got away with mistakes by benefiting from everyone else's care and attention, like a man who drinks too much but drives home safely.

No one is infallible. And those who think they are are probably going to be the most disappointed.