I think confidence - and I mean real confidence, not fake confidence or over confidence - precedes and succeeds success, in the sense that most often, it is a confident person who goes on to taste success. The success in turn reinforces his confidence.
I have also seen cases where the confidence is lacking or at a very low level and the person - much against his own expectations succeeds - that is the case where some external factor (luck) plays a role. But such situations are not common and in any case out of our control. But, such success also breeds it's own form of confidence.
I have heard that monks who have renounced the world develop the capacity to remain indifferent to success and failure and live a life where they remain detached from all these happenings and neither feel dejected or elated. Such a frame of mind would be very different and I wonder whether confidence is a necessary ingredient for their successes.
But for us mortals in our mundane existence, confidence and success, I would think, go hand in hand.