From “But Enough About You… ” by Emily Yoffe, Slate.com (March 18, 2009):
These days, "narcissist" gets tossed around as an all-purpose insult, a description of self-aggrandizing, obnoxious behavior. Unfortunately, the same word is used to describe a quality that comes in three gradations: a characteristic that in the right amount is a normal component of healthy ego; a troublesome trait when there is too much; and a pathological state when it overwhelms a personality. Narcissism fuels drive and ambition, a desire to be recognized for one's accomplishments, a sense that one's life has meaning and importance. The problem occurs when narcissism becomes the primary principle of someone's personality. Its most extreme form is narcissistic personality disorder, a psychological condition that impairs a person's ability to form normal relationships and wreaks havoc on those who have close encounters with it.
A recent study titled "Leader Emergence: The Case of the Narcissistic Leader" describes how narcissists have skills and qualities—confidence, extraversion, a desire for power—that propel them into leadership roles but that when true narcissists are in charge, other aspects of their makeup—a feeling the rules don't apply to them, a need for constant stroking—can have "disastrous consequences."