Philip Roth has just announced he has written his last book. He is 79 and has won every literary prize except the Nobel. With 20 books to his credit it seems likely that he's said everything he has to say. Perhaps his imagination has run dry and he doesn't expect another flow of creativity. Okay. No dishonor in that. Why go on writing if you've said it all? As I've said in my newspaper column on writing, it's better to stop before you start repeating yourself, or, worse yet, produce mediorce work. E.M. Forester quit in his 40's, apparently. Harper Lee and Giuseppe di Lampedusa wrote only one novel. Boxers and writers should retire before they make fools of themselves.