There’s one of Ron Weasley. It says: “Ron Weasley taught us that you can overcome your lack of confidence if you believe in yourself.”
That sounds like B.S.
Belief is an opinion or conviction. It’s faith in the “truth of something not immediately susceptible to rigorous proof.” Belief is concerned with the unknown.
Confidence is based on what we know. On what we understand.
Self-confidence comes from a knowledge of your own strengths, weaknesses, tendencies and capacities. Self-belief is some mystical faith in the power of you.
Both are necessary, but blind belief is never a substitute for sound self-confidence.
If you lack confidence you don’t need to believe in yourself. You need to understand yourself better.