I have many times complained about voiceover in films. Memento is one film that absolutely lives and dies with its narration, and its black and white framing story (if you can call it that), as much as its story-in-reverse gimmick.
And, I'm inclined toward a personal tangent right away. Sorry. But, in terms of Leonard's (Guy Pearce) choice to reside in a motel, having spent more time in motels in the last few years than I had in the last couple decades, I've got to say, staying in a motel is not a good way to create any real continuity in your life. Every day in a motel seems the same. If you don't put out the sign to keep the cleaning crew away, your room will be neat and your bed will be made when you've been out all day. Your stuff will still be there, but the mess and the clutter won't be so messy or so cluttered. It isn't obvious in Groundhog Day but it's the specificity--or lack thereof--of where his stuff is in his room at the Cherry Street Inn that indicates for Phil that it's not the next morning, but a resumption of the morning previous.
(Speaking of Groundhog Day, Sammy Jankis--Leonard's way of explaining his condition--is played by none other than Ned Ryerson himself, Stephen Tobolowsky. Sammy, of course, fakes recognition, while Ned ecstatically celebrates the real thing.)
Or maybe the simplicity of the motel room is the point. There are no distractions, no extraneous decorations to draw the eye away from a handwritten note on a paper bag--SHAVE LEFT THIGH. Leonard is, after all, purposely existing in a world where he isn't make new memories. Whether or not he can, he has chosen to refrain because that is the only way he can deal with life without his wife. Just now, he told Natalie (as she's falling asleep, so cinematically, this is truth):
I don't even know how long she's been gone. It's like I've woken up in bed and she's not here... because she's gone to the bathroom or something. But somehow, I know she's never gonna come back to bed. If I could just... reach over and touch her side of the bed, I would know that it was cold, but I can't.
He can't because he has left his house behind, left his life behind, and lives only in the new habits, motel rooms and tattoos, casually stolen cars and deliberately invented realities. His truth continues:
I know I can't have her back... But, I don't want to wake up in the morning, thinking she's still here. I lie here not knowing... how long I've been alone. So now... how can I heal? How am I supposed to heal if I can't... feel time?
Like depression, like an office job, like the monotony of a life that isn't worth living, but you live it anyway. Time is relative and all that jazz. Time flies when you're having fun. Time fucks around and meanders and forgets to matter except inasmuch as it pains you when life is boring and dull. Leonard's life is decidedly not boring or dull, but he choose the repetition, chooses to make for himself a life only worth living in meaningless chunks. His tattoos tell him a story with details missing so that he can interpret it however he needs to at any moment...
But, how is that different from any of us any day? Inventing life moment by moment, keeping what works, trying to forget what doesn't. (As Teddy says, "So you lie to yourslef to be happy. There's nothing wrong with that. We all do it.") Leonard is just better at the latter, not so great at the former... except going by--and I think I've mentioned this at some point in this blog before [yep]--Clark and Chalmers' (2000) notion of the "extended mind", Leonard's notes are a part of his mind, a part of his identity. They are just as much him as memories would be. And, since he cannot make new memories, the tattoos become memory, become fact. He tells Teddy (Joe Pantoliano), "[M]emories can be distorted. They're just an interpretation, they're not a record, and they're irrelevant if you have the facts." In Leonard's world, though, facts and memories are one and the same.
Because of this, Leonard's character can remain consistent, while Natalie (Carrie-Anne Moss) can deliberately manipulate him by playing a part, giving him new "facts" to act on. Same with Teddy--use Leonard's condition to deal with whomever. Incomplete details mean there are gaps to be filled in. Like any mystery, or any movie. We fill in the gaps to understand and connect with the characters. Here, Teddy and Natalie fill in those gaps to manipulate Leonard. We're just along for the ride. One more step removed from the filmmakers than usual.