My favorite of Shannon’s short stories, probably because it has some philosophical issues nicely woven in. Percy, of course, deployed “what if” devices in his novels and non-fiction:
One can’t read of that [Civil] War without playing the fascinating game of what-if . . . What if Jackson had lived through Chancellorsville? What if McClellan had listened to Phil Kearny (instead of to the Pinkerton detectives) during the Seven Days? What if Jeb Stuart had tended to business at Gettysburg?
Walker Percy, “The American War” (1957) in Signposts in a Strange Land, 1991, p. 74.