Forgetfulness
I spotted this image on Tumblr the other day and it reminded me of a story. A couple of years ago, I was reading a Harry Potter fic in which Harry inspired to become a ninja by watching the anime series Naruto. (Never mind that the Harry Potter books take place in the 90s and the TV series premiered in 2002.) Anyway, I came to a chapter in which Harry pulls a prank by using genjutsu to make some of the Hogwarts professors to reënact a scene from The Wizard of Oz. This sort of "prank" turns up pretty regularly in Harry Potter fics, especially in rebellious!Harry stories like this one, and it always bugs me. Magical mind control is a big no-no in the Harry Potter universe, and just because it's accomplished by way of a potion or genjutsu or whatever doesn't make it any less unforgivable than the Imperio Curse. So I left a review for the author saying just that.
At least, I tried to. When I submitted it, I got an error message saying I'd already reviewed that chapter. Which was ridiculous, because I knew this was something I'd never read before. Obviously a bug in the system. So I left the review on the following chapter instead. Once I finished the story, I looked over some of the earlier reviews, and found, much to my surprise, one I'd left two years earlier. On the same chapter, on the same topic, saying pretty much exactly the same thing. Granted, I was reading a lot of HP fic in those days, and I certainly can't claim to have a perfect memory, but nevertheless it was a little embarrassing to see just how thoroughly I'd forgotten about it. Not very flattering for the author, either.