Lady Macbeth comes across as more unscrupulous and ruthless than her husband, but since he had decided been connived by the witches into believing that he would become king by greeting him with the title 'thane of Cawdor' and saying that he shall be 'king hereafter,' it did not take too much for her to persuade him to commit the most grievous of crimes - the ultimate betrayal.
Macbeth expressed doubt about murdering his king and cousin since, as he reasoned, he was too close to him - Duncan was his kin. Added to that was the fact that Duncan was a guest in his castle and needed his protection, not his rancor. He had been such a good and noble king, that there would be a terrible outcry if he should be found murdered. Macbeth then told his wife: 'We will proceed no further in this business.' She however, was insistent.
At first she asked what had happened to the hope that Macbeth expressed when he first decided to perform his evil. She rhetorically ask whether it was borne out of inebriation. Was he not at full composure when he declared that he would kill Duncan? She stated that she would henceforth adjudge his love on that basis. She thus placed him in a very uncomfortable situation: in order to prove his love for her, he had to carry through what he had promised.
She then questioned his courage by asking him if he had more nerve to speak about murdering Duncan than in actually performing the act? She asked whether he would rather obtain the crown than live thinking about his cowardice. She compared him, in this sense, to the cat in the adage who desired to have fish but was too afraid to wet its feet. Macbeth, in his defense said that he would do everything that a man is supposed to do, and even more. There was none who would do more than he.
Lady Macbeth was unrelenting and asked him what 'beast' had possessed him to break his promise. She stated that when he had made the promise, he was more of a man than he was at that point, and for him daring to be more than what he had been, would make him more of a man. She mentioned that when he made the vow to kill Duncan, neither the time nor the place had been an issue, but now that the conditions were ideal, he suddenly relented. She said that his fear had made him a coward and, using a horrific metaphor to illustrate how strongly she felt about making a promise, she said that she would pluck a suckling babe from her nipple to bash out its brains if that is what she had promised to do.
Macbeth still expressed doubt and she guaranteed that they would not fail. Lady Macbeth showed just how wicked and scheming she actually was by describing a carefully constructed plan for the king's murder. She told Macbeth that she would get Duncan's personal bodyguards drunk by plying them with wine and ale. They would then be indisposed and the king would be fast asleep after a long journey. This would give them the ideal opportunity to commit their treacherous deed.
Macbeth expressed pride in his wife's 'undaunted mettle' (bold resolve) and was finally convinced. He suggested that they smear Duncan's blood on the daggers of the sleeping guards to implicate them. His wife added that they would make a loud clamor at the discovery of Duncan's death so as to avoid suspicion falling on them. Macbeth then expressed his determination to proceed and asked her to put on an appearance of goodness and conviviality, for: 'False face must hide what the false heart doth know.'