True. I guess my problem is that we don't know exactly how much of Sammy's story really happened to Sammy, how much of it came from Leonard's life, and how much of it was simply invented by Leonard.
In Leonard's telling of the story, Sammy's wife is told that her husband's problem is mental, not physical (as shown by his inability to condition himself), and so she believes that there is hope, that she can snap him out of it. The death of Sammy's wife depended entirely on the fact that physically, he should have been able to make new memories.
Now, if we assume that everything that happened in that story really happened to Leonard...why did Leonard's wife test him with the insulin? After all, Leonard's condition is physical, not mental - he can, and does, condition himself to do things a certain way - so his wife wouldn't have misunderstood his condition in the way that Sammy's wife did.
I know I'm overthinking it and that it's much of a stretch to assume that even though it was physically impossible for Leonard to mske new memories, his wife thought that she could snap him out of it. I just love analyzing this movie.
