Just curious, have you ever had a moment where you make a very dumb gaming mistake.
Last time I made one in wing commander where i did a mission perfectly killed a destroyer and killed a lot of kitties but accidantly hit the load button and loaded the previous mission and have to do it all over again.

Oh yes, load or quick load buttons are classic. My stupid game mistake was when I chose to play mage against my wife's barbarian in Heroes of Might and Magic 5.

Starved to death while playing Dungeon Crawl Stone Soup because I was burning through enemies so fast I forgot to check whether my character was hungry or not...and I had tons of food.

Tons, especially on beer night. :-)

And especially with Guild Wars, since I'm going for the Survivor title - "Oh, I can take a few more hits, no need to panic..."

*thud*

"Dammit".

Believing the box hype on a few games: "Play as any character you want! Multiple ways to win!" Which is great, so long as your character fits one of those multiple ways. It's like, "I made a reasonable character the way I wanted to, and now 2/3 of the way through it's impossible to get past this part of the story." Game over. Start fresh with the formulaic uber-mage or -fighter.

I`ve killed myself countless times. It usually involves explosions.

And sometimes it's on purpose. I just looooove them explosions.

Yesterday, playing Grimrock. There was quite a hard fight which I already had to reload few times. This time I was finally winning but I had all characters badly injured. I casted Poison Bolt across large room to finish off enemy and intended to move to avoid being hurt. I quickly moved but accidentaly step exactly in the way of my own poison bolt and got 3 of my characters killed. :-/

Back when I played Halflife 1 for the first time, I quicksaved while I was inside one of those pits in Xen that spits you, like, 50 feet into the air. It took me awhile to figure out how to activate cheats so I could make myself invincible to survive the fall.

I think one of the ones I made that sticks out in my mind is from the first time I played Fallout about 2 years ago. I remember I had costumed my character out and made him all I wanted him to be. I made him pretty darn powerful and decided for more power I should join the Brotherhood of Steel. I had been saving often in that game and once I got to the highly atomic the Glow area I did a save inside, my problem was I did not have a backup save besides that. I found that I could not leave the area without dying from radiation so I had to start all over again. That day thought me some valuable lessons, most importantly to keep at least two saves in a game like that.

I've done the same thing, only with fire and ice. One time I 'walked into it' going backwards. Which made no sense. I hope they fix(ed) that bug.

I once tried to play World of Warcraft drunk. My guild was very entertained, but the day after I realized that I had burnt through a lot of gold due to the constant need for repairs. In my defense, the 2 & 6 keys are very close together.

I tag Doctor in Fallout 2, it's a great skill!

Clarification:
You don't really need any skills in the beginning. I tag Speech, Lockpicking and Doctor.
Get Speech to 100% immediately. I play most of my games with Small Guns, but there are so many books around in the world that you can get Small Guns to 100% while you're in Vault City.
Having high Doctor skill lets you heal you and your party members. With +50 exp with each successful use of the skill, you can really rack up a lot of experience in the early game. Use First Aid for the same effect, though you only get 25 exp for successful use of the skill.
You also get to heal Bessy in Modoc for extra 200 exp I think.
You also get a bonus to your stats + extra exp from the Vault in Vault City (Vault City Medical Training)
Lockpick all locked doors and chests.

All of this really accumulates over the course of the game, but it especially makes the difference in the early game.

Exactly the same thing happened to me on my first playthrough!

Early game of Hearts of Iron 3, playing as Russia.

Put a lot of effort into building tank and motorized divisions, expanded the Air Force and nearly doubled the size of the Navy.

Germany attacked around the historic date and cut through the defences like a hot knife through butter. Then I realized I hadn't upgraded any infantry divisions and 90% of my army was effectively junk ☺

The only game worth worrying about your mistakes is the game of life.

Feh. Now that the cryptics are out of the way, Arcanum. I kept trying to fight the wolves at low levels. It became very damn clear that even if I have higher levels, numbers can win out, even if the difference is just one person.

Playing Morrowind, I barely touched the main story. I wander around the whole map doing anything and everything I want and can find or think of. I find this strange crypt in the far northeast, inside is a rather insane nordic man. I spent a couple saves to kill him only for the whole game world to shake and tell me it's now impossible to beat the game. What the balls?