I need a word that means to have great potential but won't go through with it?

Question

Context: I'm a very good vocalist and I do want to be famous but not by pursuing myself as a musician because performing live at concerts is not my kind of thing.

I fear that although being a local artist isn't so bad, my songs will attract the attention of world tour artists who want to work together. That kind of fame comes with modelling, famous talk shows and so on but I feel really shy around cameras. Even though I feel I have a million-dollar-talent, I just don't feel “cut out” for appearing in public.

Answer 1

Underachiever:

Someone (such as a student or athlete) who does not perform as well or work as hard as he or she can.

E.g.

Junior is working below his level, so he's an underachiever. That's his disability. The big question is, what do we do about it?"

Answer 2

You are getting cold feet.

(A beautiful voice is a gift to all who hear it. There are many ways to share your voice with others, that wouldn't put you in the international limelight.)