I'd like to think that creator sometimes creates the artwork not out of nothing but sort of catches it hovering some place and actualizes.
You've heard that the brush of the painter or the pen of the writer supposedly is sometimes moved by some other being or force. The force to which the artist can attune herself only while being in the certain state of mind, when she's "worth it".
Perhaps the Muse flies by and dictates what to write? Perhaps the Muse tells the improviser what to play. I can say from experience that I played my best improvisations in the moments when I didn't planned them and even don't remember them after the performance.
Is there some dimension where art exists before we even create it?