Brian Tracy argues that thoughts are the only thing you fully control, and changing them changes everything else. He cites Henry Ford: belief determines outcome. Tracy says to discard self-limiting beliefs by acting as if they don't exist until they actually disappear.
Chapters
There's only one thing in the whole universe over which you have complete control, and that is your thoughts. If you wish to change any of the conditions of your life, you have to change the thoughts that precede those conditions. You have to change what is going on in your mind. Take full and complete control over your thoughts and keep your thoughts on what it is you want. Make them positive causes. The conditions or effects will take care of themselves with the inexorability of a law of nature. If you believe something, something that is positive or believe something that is negative. Or as Henry Ford said, if you believe you can do a thing or if you believe you cannot, you are right. Our beliefs do form our realities. To the degree to which we believe anything to be true, our beliefs act as sort of like a screen. They filter out any information that is inconsistent with our beliefs. However, if we begin to change our beliefs, we begin to change our realities. They exist only in your own mind. And one of the starting points of great achievement is to start questioning those self-limiting beliefs and throw them off and act as if they did not exist. And when you act as if they didn't exist, lo and behold, they simply disappear.