You come finally to believe anything you tell yourself often enough-even if it is not true...

If you repeat something over and over to yourself, your subconscious mind will eventually begin to accept it as fact. When something has been accepted as truth by your subconscious mind, it will work overtime to transform the idea into physical reality. You can take advantage of this by programming your mind to think positive thoughts. Use self-motivators or affirmations to persuade your subconscious that you are capable of doing anything you wish. Repeat the self-motivator several times a day until it becomes an automatic reaction to recall a positive phrase whenever you begin to doubt yourself. Replace "I can’t" with "I will!"

 -Napoleon Hill