I believe that basically you write for two people; yourself to try to make it absolutely perfect; or if not that then wonderful. Then you write for who you love whether she can read or write or not and whether she is alive or dead.
— Ernest Hemingway to Arthur Mizener, 1950 Selected Letters, p. 694.
I got it from Hemingway on Writing which is a short and pleasant read I’m going through right now. It turns out Hemingway was 64 years ahead of me in his advice about who to write for.