Public opinion, a vulgar, impertinent, anonymous tyrant who deliberately makes life unpleasant for anyone who is not content to the average person.
Also, I need deadlines, just like everybody else, especially coming from magazines, newspapers, and stuff like that. I need daily or weekly deadlines to get stuff done, or I continue to do things and not go off on a year of unproductivity.
Lists of books we reread and books we can't finish tell more about us than about the relative worth of the books themselves.