Nothing can permanently please which does not contain in itself the reason why it is so, and not otherwise.Before the days of the internet I searched for it in every bit of Coleridge I could get my teenage hands on. I eventually gave up the search, imagining that maybe it was just something Malamud attributed to Coleridge, but only today I discovered that it is from Chapter XIV of his Biographia Literaria.
I had my brother translate it into Latin, and I used to keep it in my flute case, written in my teenage calligraphy. When I stopped playing the flute those words remained etched in my brain.
The right notes are the ones that are there because they are the best notes for the purpose at hand. The best composers always used the right notes. One thing that puts Mozart in the highest compositional echelon for me is the fact that you just can't make anything he wrote "better." If you play a wrong note, even if it is in the chord, even if it is the same pitch but in a different register, it is never as good as the one that Mozart picked for that musical moment. When you come across something strange in a piece of Bach, the solution that follows always makes the moment that was strange make sense. It always shows why it is so and not otherwise.