It's pretty much the biggest cliché in storytelling. Want to rejuvenate your character? Just add amnesia, and poof! They become a new person. But sometimes amnesia actually works as a plot device. Tell us about the one time you thought it was the perfect trope for telling a science fiction or fantasy story.
My pick for awesome amnesia story is a classic, but it's still fantastic. The Bourne Identity, which is a techno-thriller right on the edge of being science fiction (sort of like James Bond) and manages to make amnesia a vital part of its central plot. It's not being used to reboot a tired character, but to introduce us to him. And missing memory becomes fundamental to who he is, turning amnesia into a kind of metaphor for PTSD — and making Jason Bourne even more badass in the process.
What's your pick for a story that used amnesia well? Yes, yes, we know that the way amnesia happens in fiction is rarely scientifically accurate. So grumble about that if you will, but also tell us about when this trope has been used well, and why. Include pictures, video, links, and your repressed memories!