When I was a kid, my brother and I shared a PS2. I was playing FFVII,and had played up to the final boss. I saved the game, because I wanted to go back and do some side quests I had skipped on the way there before finishing it. I leave the disc in the system, with the game case right beside the system. Next day, I come back, there's another game in the system, and disc 3 is not in the case, or anywhere nearby. After questioning my brother, all I get is "I dunno". Super pissed.
Cut to about a month later, after my brother cleaned his room and found the disc. I get it buffed up pop it in... and my save file is gone. Wiped out. Asked my brother about it, "Oh, I thought you wouldn't need it anymore." Mega Super Pissed. Of course, I should have expected that kind of thing. This was the kid who, when he was about 7 or 8, thought playing with matchbox cars meant taking a hammer to them and seeing how far the pieces would fly.