I was in a parked car listening to this song watching a confused, homeless, mental looking dude who looked like he was looking for something, just wandering around, seeming to get sudden bursts of purpose and then forgetting what he was going to do, looking into stores.
It made me think of the lost keys as broken brain synapse paths (or something anatomically correct to that effect)... like, when you lose your keys, thats losing access to at least your car and home, as well as mail, safe deposit box, other persons house etc... just by losing your keys you're cut off from all those things, though the things themselves aren't lost or even affected in the slightest. VERY frustrating, but probably no where near as bad as that old insane dude i saw wandering the streets stuck on a loop.
Also reminded me of something I once heard about goldfish, that they're memory only lasts 30seconds before it resets. When they're fucking, they've been fucking for their whole life, same with eating, or anything else, including death. Goldfish go out thinking that their whole life has been dying.
I'm not saying this sheds any light on the lyrics, but it does set the stage nicely.