Throughout the picture Leonard recounts the story of Sammy Jankis, a man with apparent short-term memory loss who accidentally kills his wife. Leonard turned down Sammy's claim, saying his condition was psychological rather than physical, which confused Sammy's harried wife. Was her husband faking or not? So she tests him. A diabetic, he administers her insulin shots, and she orders three in a row. She wants to jog his memory; she wants him to snap out of it. He doesn't. Wife dies, Sammy winds up alone in a ward. Sad, sad story.

Yet, according to Teddy (and a few frames of flashback), most of this isn't Sammy's story at all; it's Leonard's. Leonard's wife survived the assault. She was the one who had trouble with his short-term memory loss; she was the one who gave him the insulin test, which he failed, and which killed her.

Leonard has such trouble digesting this information that he decides to cover it up, ultimately by killing Teddy. He writes a note—the infamous "Fact 6," Teddy's license plate number—which will lead him to kill Teddy in the end (or the beginning). This is brilliant stuff. Throughout the picture we're trying to figure out which of the characters are taking advantage of Leonard's condition. Most are—from Teddy to Natalie to Burt, the motel manager—but the most egregious example turns out to be Leonard himself.