Hartline was awarded the Nobel Prize in physiology and medicine in 1967. Much of the details of his life, personal and professional, have been omitted here. I’ve not mentioned his wife or children, his interest in Astronomy, his failed attempt to be a Physicist. Here I’ve highlighted two important discoveries, both explored within the lateral eye of Limulus, both done in conjunction with research conducted at the MBL, and both happy accidents. These stories of Hartline should do more than teach us a little bit about vision: they should teach us a little bit about the process and progress of science. Surely a scientist must be driven, must be educated, must have access to marvelous facilities: but we should never forget the elements of chance and luck which permeate our lives, scientific or otherwise. Hartline’s genius was largely in taking advantage of his luck: his lucky access to experimental animals, his lucky access to a vibrant community of scientists at the MBL, his dumb luck in using adult Limulus to study single nerve action potentials, and the lucky chance that brought a careless co-worker into a dark room to turned on the lights.