In Macbeth, Macbeth is the tragic hero, conflicted in his quest to become king. After the witches prophesy that he will be king, he becomes obsessive when the first of the witches revelations is realized. When Duncan's men tell him that he will be Thane of Cawdor, he is both delighted and disappointed. He desperately wants to be king and intermingled with his initial excitement at the witches' claims is a sense of dread that "this supernatural soliciting cannot be ill; cannot be good," as he says in Act I, scene iii, line 130. Even Macbeth is shocked by his own thoughts and the "horrid image" (135) that he conjures.
In scene v, Lady Macbeth hears the news and is equally excited and determined to see it through to the point that she will go to any length to remove any obstacles that stand in Macbeth's way. She is especially concerned as she is not sure that Macbeth's ambition is enough, suggesting that he is "too full of the milk of human kindness"(I.v.14), meaning that he is not cold and calculating enough to see it through.
In Act I, scene vii, Macbeth considers his position. He understands the consequences and recognizes that murder often comes back to "plague the inventor" (10), meaning that the murderer will be hounded himself after the event. His reasons for not killing Duncan include the following:
- Macbeth states that he is Duncan's "kinsman" (13), suggesting a family relation and also that he is Duncan's "subject," thereby falling under Duncan's dominion or kingdom—certainly good reasons not to murder him, as he says, "strong against the deed" (14).
- As Duncan's host, Macbeth is expected to protect Duncan against anyone plotting against him, his "murderer" (15), and not be the one to carry out the deed himself or "bear the knife" (16).
- Furthermore, Duncan is a good king, "clear in his great office" (19), indicating that he has done no wrong and "has borne his faculties so meek" (17) as to not deserve such a fate. Macbeth therefore realizes that anyone who murders Duncan will surely suffer "deep damnation" (20).
Macbeth goes on to state that the only thing that makes him even think about such a "horrid deed" (24) is his "vaulting ambition" (26), which he recognizes as a character flaw so strong that it may "fall on the other" (27); it is so encompassing as to be his downfall.