Believe that nothing is impossible. The universe says only two things are impossible: perpetual motion and violation of causality. In other words, everything runs out of energy and you can’t reverse the flow of time.
If it’s been done before, it can be done again. It may be difficult and it may require more than you’re willing or able to give, but whatever you want can be accomplished.
You’re probably missing out on some of the best things in life because you believe that it’s impossible for you to have greatness. Nothing is impossible. Believe this, even when the circumstances say otherwise.