"The outer world not only influences our inner world - it bullies it, it dominates it, it mesmerizes it. We're hypnotized by the outer world" - John Kehoe
We all live in two worlds - the inner world and the outer world. The outer world is where our playing is. The inner world is where our emotions and thoughts are. These two worlds are connected - they influence each other.
We are taught from when we are children to be hypnotized by the outer world. If something bad happens to us, we think about it and our attitude becomes negative. If something good happens to us, we think about it and our attitude becomes positive. It is very important to understand that the outer world DOES NOT have to affect the inner world. We can choose our own thoughts and feelings regardless of what is happening.
When we are practicing, we want to also practice the correct attitudes no matter how "difficult" something seems to be for us. Even if the practice is going badly, we want to remember to not let the outer world affect our attitude. I admit that this isn't easy, but if we can remember to practice attitude as much as finger movement, we will see that the playing will begin to reflect that attitude.
I'm not suggesting this so we can all feel better about playing badly. What I'm saying is this - the attitude of confidence, the attitude of expressiveness, the attitude of spontaneity, the attitude of enjoyment, the attitude of ease, all the positive (as well as negative) attitudes that we have when we practice and perform DIRECTLY affect our physical playing. If you want to play better, you must also practice the attitude of the great players - confidence, calmness of mind, enjoyment, ease, etc. Do not wait for your playing to be perfect in order to practice the right attitudes. Practice your attidues now with the understanding that it will directly affect your playing. In doing this consistently, you are using the inner world to affect your outer world.
Experiment and play with this idea. Have fun with it. Write down the attitudes you would like to have when playing and keep the list in front of you while you practice. Watch great performers and notice their attitudes as they play. Don't worry if you slip or become negative - just try to reset your attitude whenever you can. Keep practicing and cultivate your positive attitudes and "act as if" you are playing the way you want. If you stick with it, you will see how important this is.