People believe that memory is like a video or files stored in some sort of computer. But it's not like that at all. Memories are actually constructed anew each time that you remember something.

Each time you take an old activation sequence in your brain and re-construct it; like building a toy airplane out of Lego and then smashing the Lego, putting it back into the box, and building it again. Each time you build it it's going to be a little bit different based on the context and experience you have had since the last time you created it.