Believe your self, that is confident.

Not believe other that's is over-confident.

Confidence is based on the facts and figures and overconfidence is based on speculation.

First we analyze that work, then decided we can do that work this is confidence. Without analyzing that work then decide we can do that work is overconfidence.

Confidence is when you commit that you can do that work in the given time and you do it.

Over Confidence is when you say a lot about yourself and you show nothing.

Confidence literally means reality. We don't need to talk, the result of our work will give the answer to every question.

Over confidence is virtuality. We imagine more than what really happens and over talks about everything.