To me, the root of self confidence is derived from this quotation,
"Without self-confidence we are as babes in the cradles. And how can we generate this imponderable quality, which is yet so invaluable most quickly? By thinking that other people are inferior to oneself.”
Virginia Woolf (1882–1941), British novelist. A Room Of One's Own, ch. 2 (1929).
In my mind, thinking that other people are inferior does not mean that I am looking down on them. Each one of us has our individual strengths and weaknesses and knowing these strengths and harnessing it, either individually or in a team could prove to be a successful combination.
Self-confidence also comes from practice, especially where public speaking is concerned as not all of us have the courage to go out and speak to a large crowd. It needs courage. This would apply in other skills, ie, practice doing what we love and improving on it gives us pleasure that we can easily achieve anything if we know we can!