FF VII comes to mind. Spent a few hours grinding AP and EXP at North Crater to get every materia and character to max level. Didn't save during the grind. As I was finally heading back to the save crystal, a battle with one Ahriman started. For some weird reason, maybe out of boredom, I tossed a random battle item at the Ahriman, which triggered it to counter with LVL3 Death. Whole party was KOd because I had just achieved lvl99 with everyone. I just sat there watching the game over screen with blank eyes for a while... and started over. Felt nice.