I was running Deathwatch, and Deathwatch is kind of a fundamentally broken game. More, you need people with a very specific mindset to play a Deathwatch game, and there was one player who just didn't get it. He just couldn't wrap his mind around the Imperium, he kept thinking he was fighting for the Federation of Star Trek.
He really got it during a mission when the Kill-team landed on a tyranid-occupied planet to steal a vial of anti-tyranid virus. They were joined by a group of guardsman and their hard-as-nails Commissar, who had survived the fight in spite of the world turning to acid around them. They were battalion-strength, their number diminished over the course of the mission, and then they were down to about a platoon worth of men. The Space Marines got the vial and were about to evacuate, when the Thunderhawk gunship arrived. A Thunderhawk can hold, at most, four sections of men (about forty men). Of course, everyone started scrambling to get on it.
The Commissar, however, insisted that NO ONE would get on the ship except the Space Marines. The Space Marines had to succeed, no matter the cost. He shot the first man right in front of their eyes. The one PC who didn't get it said "Is he coming with us?"
But no, the Commissar wasn't coming either. It was literally just them. The five Space Marines were the only ones who were going home on the super-Thunderhawk, because any more than that number would jeopardize their escape. The PC was like "Oh my God, now I get it. I really fucking get it" and it was marvelous to see.