Man, that happened to me when I was young. I was very far on FF7 then I lent the controller to someone who wanted to try while I was needed for something then when I come back, I noticed my save was overwrite by that guy (which BTW, did a new game).
That's why, up until now, I still never finished FF7 story because I was so pissed off that I didn't want to redo it entirely.

One of my cousin was victim of the same thing on Pokémon Ruby (GBA), he wanted an all dragon type team so I gave him my Latias which was Sapphire exclusive.
Then one of his little cousin wanted to try too, so you can guess what happened afterwards when he did a new game...

Never had this happen, but in a similar vein my ds would flip out and delete my etrain odyssey save data. My presumption was that the cartridge reader wasn't working properly and would constantly read things incorrectly then assume they were corrupted. Lost the last stratum for 1 and 2, while 3 got cut during the playthrough for the true end. Managed to save soul silver though when it tried to do it to Pokemon. orz

I did this in Xenogears to myself. My brother and I both were playing it, and he'd left his game running, so I just went to save it so I could play, but by sheer muscle memory, I saved it to my slot... >_<

I had this done to me back in the day... i learned quickly to make multiple save games to avoid future issues.

Braxat51 said:

I had this done to me back in the day... i learned quickly to make multiple save games to avoid future issues.

Always, always, have backups.

Feather7603 said:

Always, always, have backups.

And backups of the backups. I always save to at least 3 separate slots to make sure I can't overwrite by accident or in case I need a 'just to be safe' save from 3 hours ago.

sporked said:

And backups of the backups. I always save to at least 3 separate slots to make sure I can't overwrite by accident or in case I need a 'just to be safe' save from 3 hours ago.

Doesn't always save you. (Well, not enough, anyway...)

I had a game of X3:Albion Prelude get wiped back 100 hours because I didn't realize the data was getting corrupted on saves in a way which didn't become apparent until much later. I had just overwritten my secondary backup (of about 20 hours or so of gametime) with a new save, leaving only the relatively ancient tertiary backup intact from before the mod that wound up causing the corruption was installed...

NWSiaCB said:

Doesn't always save you. (Well, not enough, anyway...)

I had a game of X3:Albion Prelude get wiped back 100 hours because I didn't realize the data was getting corrupted on saves in a way which didn't become apparent until much later. I had just overwritten my secondary backup (of about 20 hours or so of gametime) with a new save, leaving only the relatively ancient tertiary backup intact from before the mod that wound up causing the corruption was installed...

Ewww, nasty. Yeah that's about the only totally unavoidable type of save loss. I had the same thing happen way back when on the very first X game when it had only been out a few weeks. I had just gotten to Argon space and lost all my progress because of that 'creeping corruption'... maybe its something to do with Egosoft saves in general as well as mods interfering