When running for office, the most useful attribute you can have is to believe that the world absolutely, positively needs YOU!! in the position you seek. The process of running is simply too ghastly to tolerate if you don't have a good dose of this sort of egotistical self-assurance.
Most successful politicians have this. I evaluate candidates I might work for in part by looking for this useful monomania; if they haven't got it, they will have a much harder time winning. Sometimes good people who are more reflective than the perfect candidate still make it into office, but in highly contested races, exaggerated egotism helps. Being a candidate is about playing a 24/7 theatrical role, seeming to attend to and happily interact with all-comers. It's most readily accomplished by people who can excuse something less than complete personal candor in service of what they generally believe is a higher good: their own victory.
Does surviving this ritual give us the best people in office? That's something I think about a lot. Policy experts -- wonks -- tend to make lousy candidates because they think too much. But we need people in government who can explore and evaluate problems they don't know about yet. I don't have any answers.
Here's an example of the candidate's fate, not an uncommon one. It couldn't have happened to a more deserving egomaniac, though Newt Gingrich doesn't seem to handle it all that well.
"You're an embarrassment to our party. Why don't you get out before you make a bigger fool of yourself?"says this Iowa voter.
H/t to Paul Waldman at TAPPED.