Walker Evans once wrote a friend: "Stare. It is the way to educate your eye, and more. Stare, pry, listen, eavesdrop. Die knowing something. You are not here long." Evans’ insistence on staring as the main road to learning included making pictures of subway riders with a hidden camera, but he felt so guilty about being an unobserved observer that he withheld publication for years. This compunction still dogs many photographers but seldom stops them.