"With this character's death, the thread of prophecy is severed. Restore a saved game to restore the weave of fate, or persist in the doomed world you have created."
Any time a critical character dies (usually because you're on a killing spree) it says that. But it's also become a meme when someone famous dies in real life.
The Elder Scrolls III: Morrowind. It happened when important NPCs died, rendering unfinished or future quests associated with that character impossible to complete or start; iirc essential NPCs didn't have immunity to damage and death in Morrowind like in later Bethesda titles, so these NPCs were protected only by the player reloading their save after getting this message upon the essential NPCs' death.