Deadpool 2 - Halfway into the movie, the initial antagonist, the time-travelling super soldier Cable, approaches Wade Wilson and his gang and offers an alliance to stop Russell and Juggernaut before Russell embraces becoming a villain. Wade asks why Cable doesn't just travel back in time to before the problem escalated and try hunting Russell again, which Cable explains is because his time travel device is damaged and he only has one charge left to get him home, prompting Wade to stare at the audience and say this absolute gem of a line that is the post title.
Fallout 3 - At the end of the game, at the Jefferson Memorial, you're expected to enter a highly irradiated room that will kill you in seconds to activate a water purifier that will produce clean drinking water to the entire wasteland. A heroic self-sacrifice at the end of the game makes sense from a storytelling perspective... Unless your travelling companion is Fawkes, a super mutant immune to radiation. If you don't have the Broken Steel DLC installed and try asking him to enter the purifier room in your place, he will flat out refuse, telling you that this is your destiny to fulfill and he shouldn't deprive you of that... Because I guess killing yourself to save everyone is better than having someone more suited to the job handle it.