Yes, that is a big part of it. Some of us on here have stated such a number of times. Yet, there is still more to it than that.
Lanny Bassham breaks down peak performance into three areas.
1) Conscious
2) Subconscious
3) Self image
When all three are fully developed and you are utilizing each optimally you are in what he calls the triad state. (zone)
When one or more is underdeveloped or temporarily not be used effectively your performance suffers
Here is a brief example of what each area refers to and how they relate to performance
Conscious- has to do with analyzing and knowledge You need an understanding of what is possible For example if you have a 45 degree cut and you plan on drawing the ball straight back then you need more knowledge You must also know the right shots for a fully developed conscious circle your strategy for the game must be tight Conscious also deals with your focus are you able to keep your head in the game and your mind positive?
Subconscious has to do with skill are your skills developed to the point to where you don't need to focus on how to do something, only what to do? For example you need to draw the ball back three diamonds, do you see and do or are you calculating how much low to use how hard to hit it and where to aim? When your subconscious is developed and being utilized the conscious is more free to do its job plus playing subconsciously is just a much more powerful way to play.
Finally there is the self image. Are you a 100 ball runner? Are you capable of running the set? Are you capable of making this shot, performing under pressure, consistently getting out, closing out the match, coming from behind, whatever. You will not be able to consistently play above the level that you believe you can. If YOU BELIEVE it's not like you to make long cut shots then you will struggle with them etc etc
You are right Neil, the self image is not the end all be all. It is one of the three ingredients but if anyone out there has been practicing and practicing yet still struggles with consistant results. Or if they play good in practice then dog it for the cash then the self image is an area of focus for them.