What can be told about music that the music itself can't tell? Only how it came to be written.

It is instructive to hear what one composer says about another because, no matter how biased, he quite knows what he's talking about. It is less instructive to hear what a composer says about himself because, no matter how sincere, he doesn't quite know what he's talking about. A composer can clarify his method to others, but not his esthetic. He can tell how he wrote his piece, but not why. His why is the piece. All else is a smokescreen through which he explains what you're supposed to hear rather than what you do hear. Unless the smokescreen itself is his music.