That is a marvelous question which provokes deeper reflection.
Some of the answers from others also stir the well.
Even if one thinks they stick to the facts, still any answer to any question will be subjective.
None of the answers given are wrong, and none are right. They are individual ideas.
As my belief systems and world views have changed into what is now, I see confidence as a quality or virtue of the divine spark in man and arrogance as an expression of the ego. Arrogance comes with a false sense of superiority, it can be a defensive mechanism from over-compensating a fear of being not enough, as the ego is caught in an illusion of separation.
Whereas pure confidence by itself is grounded in knowing who and what one is, and knowing one's place as a self-contained being in the whole of existence.