The line comes from The Princess Bride, the 1987 fantasy adventure film, spoken by Vizzini, the Sicilian criminal mastermind played by Wallace Shawn, during his battle of wits with Westley. In the scene, Vizzini believes he has won by choosing the correct goblet, only to collapse moments later after drinking poison. The quote spread through film clips, reaction videos and meme edits, where it is used to flag overconfidence before a downfall. Its staying power comes from that instant irony, a boast that is already wrong when it is spoken.