The way you act is ultimately all that matters. The only belief that matters is that if I put time and energy into getting a new skill, I actually will get better at that thing. Even if you're not going to be the greatest of all time, does it benefit you to act as if you could become the greatest? You don't read a book to check a box or go to school to impress your parents. You do it because the skill that you will acquire lets you do something in the world that other people can't do or you wouldn't be able to do. So those skills actually let you do things.