Optional actions you took that made you feel sad or guilty.
For example, letting a character die on fire emblem.
Killing someone that could be saved, it doesn't matter if you already did know that before or after you killed him/her.
Making choices you would regret later on.
Being obligated kill someone you don't want to (Pic Related ;_;)
Not completing an objective, leading to bad situations.
Or something you did to feel guilty.
Da... dad? Are you ok?
Fallout 1. Basically agreed to save a bunch of people, but once they gave me what I needed I just left them all to die.
Saving them would've been kind of a pain in the ass so I didn't.