When do you cross the line - Confidence to Cockiness?

"If you say you're going to do it, and you go out and do it, it ain't braggin." Dizzy Dean, Hall of Fame pitcher

The confidence that a successful person displays is fun to watch. They are a shining star and you want to be like them, to have that air of invulnerability, to seem to be on top of everything. But the line they can cross, to overbearing cockiness, how does that happen? Where? When? None of us really like to deal with a braggart, but there is some sort of magnetic quality about someone with inner strength and courage that you can feel. But arrogance is most often a detriment to a relationship of anykind, business or personal and should be avoided.