That negative self talk comes from thinking while down on the shot, once you get in your stance your ONLY thought should be moving your cue straight in the direction of the shot, don't even think about speed of stroke, your body already knows what to do, you have to allow it to, one of the things that clicked with me from the book was this....
You do thousands of things everyday you don't think of that require great skill and accuracy, you probably woke up this morning, got out of bed, walked to the bathroom, opened the door, turned on the light without a single thought, you didn't calculate how much pressure it would take to open the door or turn on the light, let alone the balance required to walk, how did you do it? You've done it thousands of times, you've done it so many times the subconscious part of your brain already knows how to do that, much like walking and talking, the problem comes when the conscious part of the brain tries to take over what the subconscious part of the brain already knows what to do, like thinking when I was down on the shot, for most people including me it takes a lot to learn to "let go" we are taught to think things through, when it comes to performing precise physical tasks, first calculate with your conscious brain and then free your subconscious brain to do what it does best.