The line comes from The Ballad of Buster Scruggs, the 2018 Western anthology film by Joel and Ethan Coen, and is noted here from the final duel segment. Short, quotable movie lines spread quickly as reaction sounds on soundboards and in edits because one sentence can carry the whole joke. Fans pair it with the equally dry realisation style of it was at this moment he knew, using both for that instant when a character understands trouble has arrived and there is no easy way out of it.