I accidentally activated hard mode in La-Mulana because I forgot about the warning about reading a certain mural twice. And from what I've heard, hard mode is a complete and total pain in the ass, to put it mildly. Oh, and the game doesn't tell you you've just entered hard mode, so I wound up saving in hard.
Luckily, I had accidentally (don't ask) created a backup save three hours of play time prior. Turns out much of those three hours were spent aimlessly wandering, so I didn't need to redo too much. But it was still very irritating.
Maybe I'll revisit hard mode in a second playthrough.