Final Fantasy III DS has a three-file save system. My first, "good" file had approximately 83 hours of progress logged into it. My second file, used for backup purposes, had 74 hours. My thrid file contained a recently-restarted quest in which I had last made exactly 14 minutes' progress. Having grown tired of grinding for the game's hidden superboss in my first file, I decided to make some headway in my File Three game. I soon chose to save my game as any prudent player would do.
You all should know what happens next.
Expecting the "which file do you want to overwrite?" cursor to automatically appear over the third file slot, I saved. And overwrote my first file. And lost over nine hours' worth of tedious, mind-numbingly monotonous training.
:'D