I think save/load errors are going to be the biggest problem with any game. In particular games that lack auto-save.

I was playing Mount and Blade on a Sunday and was about 5 hours in. I had a really nice character, was getting really nice gear and great soldiers. Got up to get something to drink and BAM! Chair pulled out the plug, didn't save. So I started it up again. Two hours in, BAM! Game crashes. One save at level one. I put the game away and didn't play again until Warband was released.

I quick saved Max Payne once a second before I died (molotov coctail to the head).

I tried to bullet time jump through this, but I died like 100 times, and stopped.

I'm a compulsive quicksaver in Bethesda games, so I've had many, many, MANY instances where I accidentally hit quick load while attempting to quick save after some tough battle or dungeon.

Many years ago, I got the B-Wing expansion for X-Wing. I didn't have X-Wing, so of course it didn't work. It said on the side of the box "X-Wing required", but I figured it was some sort of marketing fluff; like a racing game that boasted "Seatbelt required!" to suggest it was ultra-realistic.

Eventually I did get X-Wing, but sadly not the other expansion, Imperial Pursuit.

Divine Divinity this time around, trying to make sort of an all-purpose archer-thief.

Started a new game in crayon physics deluxe, not realizing that there is no save button and it simply saves your progress when you leave the game, so starting it anew completely deletes your progress.

I make a billion mistakes playing starcraft 2, but my dumbest was building a bunch of turrets to protect me from voidrays and any other air incursions only to realize i built them in the side of my base closest to the edge of the map and not to the side towards my opponent's base.

Oh, and standing in an elevating platform in Deus ex, pressing the button to go up, noticing I'm hearing the platform but I'm not moving upwards, until the platform comes down and crushes me.

Huh, I really had to think for this one. I know I have done some stupid things in games, but I just couldn't think of any really stand out ones. Mostly, I play single-player RPGs and turn-based strategy games, so i can just reload a previous save if I do anything too dumb.

I suppose what comes closest is playing Diablo 2 around 10 years ago on the online servers, getting around 5 characters fully equipped in the best rare gear (best rolls on the gear itself too), then forgetting to log in for a few months and having all my characters deleted. This is before Blizzard started with the ranked/rated (or whatever it is called) system, so inactive characters were just plain deleted forever.

In X2 (space flying game kinda like Privateer, but way better), at some point, you are supposed to escort an NPC somewhere.

Problem was, I already had a battleship at that point and she was in her comparatively tiny heavy fighter (think, bus vs bicycle and you'll have an accurate picture of the scale).

So, long story short, I was following her and at some point, I pushed the accelerator too far and rear ended her.

Priceless moments.

As said, while the quickload/save function can be very helpful at times, it can also perfectly ruin a good time. Like those times when one (not me; no, certainly never me =P) accidentally quicksaves after receiving a heavy beating while one meant to load instead, meaning: one's death no matter what one does. The issue becomes especially dire when one realizes one may not have made a proper save within the last hour or so. - Unreal

Or last night while playing RCT I meant to minimize the window so I could goof off in Firefox for a quick second... just to accidentally close the entire game instead... and I hadn't saved in a good while. *le sigh* Not a true gaming mistake, but still incredibly dumb.

Any game designer that puts quicksave on F6 anf quickload on F7 should be shot. Hanged, mutilated and then shot.

I remember playing Abe's Exoddus and falling off a cliff, then going to quickload but accidentally quicksaving so everytime I load I die. FAIL

Ouch, yeah those were the days that you have contansly need to go to the game or lose progress.

My second New Vegas character was a scrawny female sniper, so I made Strength a dump-stat and put it at 1. I knew this would stop me from carrying much, but what I forgot was that New Vegas has strength requirements on the weapons. I got 20+ hours in before realizing her strength was too low to effectively use the sniper rifles I was supposed to be a master with.

Felt pretty stupid.

I had made a mistake with that game as well had a hard fight and accidanly load the game instead saving yeah i know it was late and i was tired lo.

Agreed. That's why I always change to F5 to save and F9 to load if possible.

Still I screwed up more than once. It often happens when I had to try a elevated number of times to beat a enemy / situation particularly difficult. With the thrill of having achieved finally and the rush to save before the game throw something else to me... what a sad mistake!

I also remember fondly the original Doom. Save when you were on a ledge or narrow causeway, and every time you tried to load the savegame meant an automatic fall to the distant ground below...