The cellist Yo-Yo Ma, quoted in Imagine by Jonah Lehrer:
When people ask me how they should approach performance, I always tell them that the professional musician should aspire to the state of the beginner….To become a professional, you need to go through years of training. You get criticized by all your teachers, and you worry about all the critics. You are constantly being judged. But if you get onstage and all you think about is what the critics are going to say, if all you are doing is worrying, then you will play terribly. You will be tight and it will be a bad concert.
Instead, one needs to constantly remind oneself to play with the abandon of the child who is just learning the cello. Because why is that kid playing? He is playing for pleasure. He is playing because making this sound, expressing this melody, makes him happy.
That is still the only good reason to play.