As a young student, I used to believe that we musicians practice to achieve proficiency. Now, having been blessed to hear and see many of the greatest musicians of our time, I know that we do not practice for proficiency and expertise alone. We practice to become at one with our instruments: the violinist is not only learning fingerings--she is growing new limbs; the brass player does not learn only mouth position--she is learning to speak with new lips; the singer is not only strengthening her voice--she is preparing a home for the music she was made to sing.
The most beautiful music is beautiful because of this: it has become one with the musician to such an extent that it cannot help but reflect every angle of human experience. For the audience member who is willing to look in the mirror, the experience can be enormous.
The ultimate challenge for the musician is to trust that human experience, reflected in this integrated musical expression, is enough. She must not add to the reflection, or try to manipulate the mirror. She can only hollow out from within herself all judgment and tendency to control how she is reflecting to her audience, and then concentrate on the principles and the music she is "performing".
Performance, when looked at from this perspective, is really just an inaccurate way to describe the most Ego-less and sincere form of Being.