When does it dawn on you that you want to play the piano? When your mother keeps dragging you off to see her best friend, Dame Myra Hess? When the toy piano you got for your fourth birthday is the only thing you managed to save from the earthquake? Or is it when you pass a musical instruments store, suddenly begin trembling, go inside, sit down at the first bench, and, without knowing how, spin off what the astounded salesman identifies as Bach’s Chromatic Fantasy and Fugue?