Macbeth: Theme of Night vs Day and Evilness “Fair is foul, and foul is fair” (I.i.10). This becomes the key phrase in describing Macbeth's downfall. It defines the night vs. day motif, foreshadowing the evil that will soon come. The night vs. day motif is so important in bringing out the theme of evil in this play because almost all of the elements of Macbeth's downfall are revealed at night. Sleeplessness, murder, and the witches' prophecies all become relevant as the drama unfolds. When the witches tell Macbeth that he will soon be the Thane of Cawdor, his ambition b