The New Yorker.
In a review of a new book--Leonardo and the Last Supper--we learn that in his time, Da Vinci had a reputation for being a "dilatory and even unreliable worker whose career was strewn with abandoned projects." According to author, Ross King, he was as hard on himself as we can be, moaning to his diary, "Tell me if I ever did a thing." When the commission for the Last Supper came in, Da Vinci was juggling work on a giant bronze horse (never finished), various flying machines, and a joke book. For a genius, he was, it appears, quite human.