Is overconfidence the greatest enemy?

[Hardkill]

Optimists such as Tony Robbins have mentioned that it's better to be an optimist even though pessimists are about 10 times more accurate than optimists. Even people like Leo have mentioned that you always got to visualize success in order to succeed at anything. However, Overconfident or cocky people are criticized for overestimating their abilities, making an ass out of themselves, and even possibly jeopardizing their own lives. Of course it's ideal to have a healthy balance of confidence and solid self-esteem along with humility. Though, I wonder now if it is actually better to be overconfident or cocky then it is to lack confidence because you don't believe that you can succeed at something?