What is told three times is true

Shakespeare, Julius Caesar, Act I, scene 2:

Soothsayer: Beware the ides of March.
Caesar: What man is that?
Brutus: A soothsayer bids you beware the ides of March.
Caesar: Set him before me; let me see his face.
Cassius: Fellow, come from the throng; look upon Caesar.
Caesar: What say’st thou to me now? speak once again.
Soothsayer: Beware the ides of March.