In Act 4, Scene 1 of Shakespeare's "Macbeth," the first apparition tells Macbeth to beware of Macduff, but the second says he does not have to kill him if he has no reason to fear him. Nevertheless, Macbeth resolves to seize the town of Fife, raid Macduff's castle and murder him as well as his wife, children and everyone in line of succession. As a result, Macbeth expects that will help him conquer his fear and sleep easily at night.
In this scene, Macbeth talks to the apparitions. The first one urges him to be careful of Macduff, but the second one tells him that no man who was born of a woman can hurt him. Macbeth, therefore, concludes that he has nothing to fear because Macduff cannot hurt him. However, he states that he will make "assurance double sure" (he will make doubly sure) by killing Macduff. In this way, he believes, he will ensure Macduff truly does not do anything against him.
