up Isabella d’Este’s portrait, complaining of Leonardo’s ‘haphazard andextremely unpredictable’ routine. This frustrating restlessness was, ofcourse, integral to the obsessive creativity. Pacioli had been able to draw aline under a piece of work and consider it done, but for Leonardo thisrepresented a mental hurdle that he frequently failed to clear. He leftpaintings unfinished for decades – Lisa del Giocondo sat for the Mona Lisawhen she was in her early twenties, and was thirty-nine when Leonardodied, still working on it – and he evidently felt similarly about hismanuscripts and notebooks