I was genuinely saddened when on my SC:Chaos Theory play-through I accidently killed a guard in a mission (He stumbled into the room as I was hacking something and was stood next to the alarm) Wrong time, wrong place Mr. Guard
After I kind of wondered if I could have used some equipment such as the flash to give me those extra couple of seconds to disable him instead as I had decided that I wasn't going to kill anyone that wasn't genuinely "evil". - Mainly as if you listen to the dialog in the game, most of the AI seem to hate working for their bosses and some don't even know about the corruption of the organisation.
I did consider restarting my save point, but I decided that it should be a lesson to my player for not checking the other damn door to start with.
Yes, I genuinely am that sad when playing games