Your brain acts on what you expect, not what you wish. Practice is a method of conditioning our minds to respond to positive expectations. Practice is the only way to build confidence in anything. Pool is no different. It may not make you a world champion, but it will galvanize your skills against doubt and apprehension.
Champions believe with all of their hearts that they deserve to be champion.
They are right. It is no coincidence that they practice regularly, and that they are well conditioned, positive thinkers. They expect to win, and the brain does everything it can to fulfill that expectation. Now, go make that long, straight-in shot and know with all of your heart that you deserve it.