I can think of virtually no artist who has devoted the bulk of her career to a single subject. Picasso now and then jousted with his alter ego, the Minotaur. Rodin tinkered with figures from The Gates of Hell on and off throughout his long and productive life. Georgia O’Keeffe did multiple paintings of the same vistas, flowers, even clam shells. But one single solitary ongoing obsession for nearly 30 years?