Michelangelo was both fast and slow: arrancadas de corcel y paradas de burro, say the Spanish of this kind of behavior: rearing racehorse starts and sudden donkey halts.   The man who could carve the eighteen-foot-high David in eighteen months, without help, if we are to believe Vasari (probably we shouldn’t), rarely finished any other figure his whole life long.  Wherever he worked he left unfinished statues behind, most of them in a stage of blurry perfection.  Was this always due to the changes of fortune and to fickle patrons?  Obviously not.  Every artist understands this.  They all have a few perpetually unfinished works standing suggestively in their ateliers and they know why: they hate to destroy the work as it is, even in order to perfect it.  Are they afraid of spoiling it, making it worse?  That too.  It is hard to believe that Michelangelo really improved the Slaves in the Louvre by finishing and polishing them.   Their “brothers”, the Giants in the Accademia of Florence, at an earlier, rougher, stage of execution, seem more alive; just as the simple preliminary pen-and-ink sketch often seems “better”—more forceful, more memorable—than the large, finished painting it became.