From an article on human memory that includes profiles of a woman who remembers everything she's done in her life since age 11 and a man who remembers almost nothing after 1960:
The metaphors we most often use to describe memory -- the photograph, the tape recorder, the mirror, the hard drive -- all suggest mechanical accuracy, as if the mind were some sort of meticulous transcriber of our experiences. And for a long time it was a commonly held view that our brains function as perfect recorders-that a lifetime of memories are socked away somewhere in the cerebral attic, and if they can't be found it isn't because they've disappeared, but only because we've lost access to them.
That's not the case, of course. A better metaphor for human memory might be that of an almost-saturated sponge trying to sop up spilled water on a counter. The sponge gets some of the water up but also loses some of its already-captured liquid and you just sort of smear the watery mess all over until the counter is completely wet but appears less waterlogged than it was. At least, that's how *my* memory works.