So I hear you’re in a bit of a bind with your story. You need a character to do something they know they shouldn’t, but aren’t sure how to get them to do it. Well, I’ve got the perfect solution for you, no matter the situation:
Temporary memory loss.
Yes, it means that the audience will have to relearn already established information with the character in question. Yes, the audience will have to watch certain plot threads and character arcs be re-litigated. Yes, it will make the stakes feel lower. But does it matter? You’ll have a blank slate to work with!
Clearly, I have issues with temporary memory loss for the reasons described above. To me, it feels like a cop-out; a way to dance around the plot for a while, buy some time, while the characters spin their wheels. It frustrates me because I want to see the characters grow and the plot progress.
Kingsman: The Golden Circle is a recent example of this. Galahad, one of the main characters in the first Kingsmen, is killed with a bullet to the head in the first movie. It serves as a large part of the conflict in the third act and motivation for the main character, Eggsy, to save the day. So when he’s brought back to life via a deus ex machina in the sequel it retroactively dilutes those stakes. Now when anyone takes a headshot you know they can just be brought back for story convenience. Not only that, but because he no longer has his memory we have to watch him re-establish his relationship with Eggsy. A large part of the movie is also spent just trying to get him to remember who he is, why he’s important, and what his skills are. Totally robs the story of forward momentum, in my opinion.
How common is this in storytelling? Common enough that TV Tropes has over 20 different classifications just for amnesia. I think it’s much more interesting to watch well-informed, intelligent characters use their smarts to work through problems than for the plot to be pushed forward because of convenient memory loss.