Lord Macbeth was a loyal general and vassal to the King of Scotland, until three witches stoked his ambition with a prophecy: He will be King, and no man born of woman will harm him. Assured he is invincible, with no small amount of encouragment from his wife, Macbeth seizes the throne and begins a reign of terror, only ended by meeting his own end at the hands of Macduff, born of a caesarean section.
Some might think this twist to the prophecy is somewhat contrived, as J.R.R. Tolkien apparently did when he put in his own story a similar prophecy about the Witch-King, who would not die by the hand of man. He dies by the hand of a woman.
What might've been the effect on English and later world culture had Shakespeare chosen a different end to what might be his most famous work? Perhaps when Macbeth moves to have Macduff killed, he succeeds in catching and killing Macduff but Lady Macduff escapes or survives, motivated to kill Macbeth to avenge her husband and son?