My son is 5 and has recently learned to swim, but jumping off a high diving board was intimidating at first. He had seen others do it and knew it could be done. But his confidence was challenged because he hadn't yet experienced jumping off first hand and negative past experiences in the shallow end consumed his thinking. Yet what drove him through the fear, was the idea of possibilities. If he could jump off the diving board, it would make everything else in the shallow end so much easier and his confidence would return at a whole new level.
But through the entire experience I could tell the most upsetting thing to him was the idea of failure. He was more concerned with failing to try rather than the possible and unlikely negative consequences of jumping. Failing to try meant giving up on hope on the positive consequences.
Belief and hope is what helped him overcome his doubt. Now he is at peace on the diving board.
Here's a heuristic I am playing with.
(B + H) - D = F
B = Belief
For faith, belief and hope should be greater than doubt.