Fear is the greatest obstacle to learning. But fear is your best friend. Fear is like fire. If you learn to control it, you let it work for you. If you don’t learn to control it, it’ll destroy you and everything around you. Like a snowball on a hill, you can pick it up and throw it or do anything you want with it before it starts rolling down, but once it rolls down and gets so big, it’ll crush you to death. So one must never allow fear to develop and build up without having control over it, because if you don’t you won’t be able to achieve your objective or save your life.

Mike Tyson