Any goal you set yourself or the destination you see yourself getting to is ultimately experienced by your mind.
When you have an intention or goal, it is born in your mind. What world do you want to create for yourself? How you intend for that to happen or come about again will be experienced by your mind.
So if you constantly think, "i will never attain my goal or never be where i want to be", then you will create a world for yourself which seems to confirm your belief. Through not knowing you set yourself a goal to fail and when you see that goal fulfilled, it only strengthens that belief.
Self confidence or self belief functions in a similar way. If you think you are a failure, its like your goals are to see you fail but when you believe in yourself, you create in your mind a more positive view, where even if you fail in the external world, you still succeed within.
Intentions and the results/experiences of those intentions share the same source, the mind.
Jack