"If you think you can do a thing or think you can't do a thing, you're right."
So I think I am better than others around me. I am destined for something greater. Maybe. Maybe not. What have I been doing to achieve your greater goal? Believing that I can do something is important, but that's not the end of it. Unless I move my muscles to make an extra effort, I can only manage the regular run-of-the-mill success. Even if I feel I am destined for something, if must make an effort to make it happen.
It is obvious that believing in oneself is the thing that keeps one going through hard times, but it is not the only thing.