I've always tried to have characters with real and believable flaws.
My protagonist was married once. . . it didn't end well as such he's screwed up so badly that he has a really casual attitude towards relationships and has sired several kids who hate his guts because he was such a jerk to them, granted he was so burned that he was to afraid to be with them, but it doesn't change the fact that he's complete jerk-off.