In William Shakespeare's play "Romeo and Juliet," Romeo says "I defy you stars!" after seeing Juliet dead in the tomb. He is saying that he is going to defy fate, sometimes referred to as "the stars," for trying to keep them apart by killing himself to be with her.
Romeo and Juliet are referred to throughout the play as star-crossed lovers who are fated to meet a tragic end. When Romeo states that he is going to defy the stars by killing himself to be with Juliet, he is actually fulfilling the prediction of a tragic end for the couple that was made at the beginning of the play by the narrator.