"Something to remember you by." 

So Christopher Nolan's movies have alway been confusing as hell. Good to know. 

Leonard(Gary Oldman) is stuck in his own personal hell. Once he loses a train of thought it's gone. Quite literally. He cannot remember it. He's got to tattoo himself, write notes, take pictures, and do anything else in his power not to forget... or is he trying not to remember? That's just one of the many questions Memento leaves us with. 

One thing to admire about the story : The viewer is just as confused as Leonard himself. Akin  Teddy Daniels from Shutter Island or the Narrator in Fight Club, he cannot decipher reality itself from his own perception of reality, and this is conveyed expertly in the non-linear narrative. Fantastic. It's easy to understand how this movie can draw people in, and why there are so many different fan theories and discussions. There is just enough mystery surrounding it to make you want to hit rewind and draw your own conclusions.