Ryan Holiday said it the best in this article. You can read the full details there, but here is a paragraph.
" As crazy as it sounds, you don’t need to believe in yourself. That’s not what’s holding you back. Whether you think you can do something is so much less important than whether you actually can or can’t do that thing. You need to assemble a case that proves you can. You need to do the work that stands as evidence for what you’re capable of. "
