Most people have a way if living in their own fortress. They will give themselves the negative message, that they can't do something. Then the belief seems to somehow fit itself into that mode, and you stop looking for a solution.
POSITIVE SELF TALK
You need to stop negative self talk, which could turn into a self fulfilling prophecy. Tell yourself that you can do a certain thing. Do not be in a space of vagueness, a "maybe" sort of mindset. Be positive and sure of yourself, and you will actually create a self fulfilling prophecy.