Confidence is a good thing. Most of the time. It would be impossible for the greatest among us to achieve their highest potential without confidence. Imagine if Steve Jobs hadn't had confidence in himself. We wouldn't have iAnything. Or Michael Jordan? We never would have gotten Space Jam. How about Beyonce? Kanye would have nothing to complain about at awards shows without Bey's confidence...Actually, he'd probably find something.
Speaking of Kanye, sometimes confidence isn't such a great thing. It can make you do things you otherwise wouldn't or shouldn't. For example, being so confident in an answer on Jeopardy that you end up becoming internet famous overnight for the creepiest Jeopardy response of all time.