I came across another pianist's blog today: Susan Tomes. She has a great post illustrating the challenge of balancing "involvement" and "detachment" during a performance. I laughed at the end because I can so relate! I remember my piano teacher in college once told me that I needed to play with passion but not "lose control." There is a point where one must restrain one's passion during a performance or the playing will become sloppy. However, a performance lacking passion quickly becomes boring, so one must not be too "controlled" or focused solely on the technical aspects of the music. I can recall many performances, particularly in college, when I was thinking about what I was going to eat afterwards instead of being "into" the music. Invariably I would get a comment afterwards about how wonderfully expressive and focused my playing was!