At first, Macbeth felt he had no reason to kill King Duncan, because of the witches' prophecies which stated that in the future, he will become king. "If chance will have me king, why, chance may crown me without my stir." However, when Lady Macbeth found out about the prophecy that stated that Macbeth will become king, she immediately felt reason to murder him. "Is too full o' the milk of human kindness" shows that Lady Macbeth considers Macbeth to be a "wimp," and that she'll have to do this all by herself. "Leave all the rest to me" clearly states that Lady Macbeth takes control over Macbeth's thought which was not to kill Duncan, for he found no reason to. Lady Macbeth continues to convince and persuade Macbeth into her "plan" which is to kill King Duncan. Macbeth agrees to follow Lady Macbeth's thoughts and kills King Duncan. He regrets his actions afterward, which is proof that he never was willing to kill him in the first place.
Macbeth has become deeply involved with murder, and eventually kills several others. This is proof that Lady Macbeth has transformed Macbeth into being a greedy, coldhearted human being, by saying things such as "Are you a man?" She undermines his masculinity, to make him feel at fault, and have it her way. Eventually, Lady Macbeth is driven to Madness by the guilt she holds on her shoulders, and ends up committing suicide. If it weren't for Lady Macbeth, Macbeth would have never killed anyone.