I was recently listening to the
episode of Radiolab where they discuss human memory, and in one segment a neurologist was explaining how memories are not accessed in read-only mode when we remember them...each time you recall something, the memory can be modified a little...or a lot. Over time the stored memory may be altered so heavily that it scarcely resembles the original event. Such is how two people can recall the same event with starkly contrasting stories.
The episode even discusses how fake memories can be inserted into people's minds using strong contexts. Neat stuff, but a bit unsettling.
Despite all this, we humans trust our memories, and often take great offense when the accuracy of our memories is called into question. Humans are big bags of contradictions.