In every piece of writing there comes a point at which the revision process ends. This is when words have stopped being simply words -- nouns and verbs and prepositions on a page -- and have become instead machine parts. Then, to change anything at all is to make it ring five o' clock at every hour, or worse, let its sweet face linger on the watchmaker's counter, peering through a dusty screen, like the child who rubs off the window frost to see the empty blacktop packed with snow.