Shlaes: Was David Petraeus ensnared by narcissism?

It was her six-minute mile that did it. Or her youth. That's the assumption about the choice by David Petraeus, America's most revered military statesman, to pursue an extramarital affair with Paula Broadwell, who co-wrote a biography of him.

After the announcement last week from Petraeus that he would resign his post as director of the Central Intelligence Agency because of the relationship, television and the Internet have been alive with descriptions of the physical allure of Broadwell, who is 20 years younger than Petraeus.

But a woman's age or the time in which she runs a mile are probably not the primary explanations for Petraeus' actions, just as they weren't necessarily the main reasons that John Edwards or Jack Welch, for example, pursued their affairs. Age or looks matter, yet only secondarily.

The force driving all these gents is probably something stronger than sex. What likely drives them is narcissism.

In myth, Narcissus was the hunter so beautiful that he fell in love with his own reflection. Narcissism occurs in modern life when an individual suffers from a need for affirmation of his or her own importance.

All successful people nurse some vanities. But to a serious narcissist, flattery becomes crucial to survival. He will be drawn to anyone who makes him like what he sees in the mirror. Narcissists gravitate especially toward anyone who supplies that flattery reliably or, even better, assures the narcissistic feed, providing something that elicits praise from others.

"All In," Broadwell's adulatory biography of Petraeus, was a media event that delivered multiple moments of gratification.

Edwards' choice of a mistress was a video maker who was filming his presidential campaign, Rielle Hunter.

Welch chose business editor Suzy Wetlaufer. She could help Welch spread Welch, the brand, post-General Electric, better than anyone. These women aren't arm candy. They are mirrors or cameras.

Many theorists these days find some benefit in narcissistic leadership. Narcissists don't have to be unfaithful. And they are often notable for great talent. Their desperation to produce the work that wins mega-recognition can pull forward a whole company.

In "The Productive Narcissist," author Michael Maccoby argues that the egotism of executives such as Welch helps them undertake great projects and make their companies advance. Translate Maccoby's concept over to the military, and the theory fits as well: Petraeus' self-esteem gave him the courage to wage the controversial surge of troops in Iraq.

But narcissism has a dark side: It skews the judgment of the narcissist. With the news of his affair, against the rules of soldiering, Petraeus has already tarnished his incredible feats. It is this poor wager, and not the affair itself, that so many Petraeus fans resent.

There is evidence that similar damage can be wrought by narcissists in business. The presence of a narcissistic CEO tends to mean a company enjoys a lower return on assets than others, according to scholars Charles Ham, Nicholas Seybert and Sean Wang. Companies led by narcissists pay lower dividends to shareholders. They acquire too many companies due to the leader's vain assumption that he or she can add value. The silent tragedy at many companies is the growth forgone due to the vanity of chief executives and another mirror, the board of directors.

To categorize someone who has achieved as much as Petraeus has feels wrong. Yet it isn't a bad idea to try to understand narcissism -- or vanity, the Victorian label many of us prefer.

Although most of us hesitate to diminish our heroes with labels, we can be assured that others quickly pick up the vulnerability of the narcissist and won't hesitate to exploit it. At the CIA or in the corner office, the boss who doesn't recognize his own narcissism and combat it is ceasing to be worthy of his rank. He is a leader on his way to becoming just another case.