Think of the best piece you've ever heard, well you could write something far better, not right away neccesarily. I've found this true because i'm not an espicially good pianist at all; although my teachers say i'm talented and very good...well I pay them. I've thought this to be true because the ability to compose music that is complex and gourgeous has to do with the enviroment around you, in perticular the sounds, and things that you can describe. Listening to music is a big determiner of how you're music sounds. I don't know how all of a sudden you can get this all onto the piano and make beutiful music...but I'm going to find out! Science and logic holds the truth.
The Human brain, is the answer.