Which makes me think of that idea you sometimes hear being expressed about painting - that you could throw away the end result because 'it's the process that counts'. That doesn't seem quite right somehow, because in painting you're working with materials in order to bring a material object into being. Music doesn't have that kind of materiality.
I love Rumi's idea of 'not opening the door to the study'. This poem is on the cover of a wonderful piece of music (which you can hear here http://www.youtube.com/watch?v=UEWFc4avub0 ) which was created by Ry Cooder and Vishwa Mohan Bhatt in the middle of the night, half an hour after they first met, with no rehearsal.