One of the main conflicts in the play is the one between Macbeth and his wife, Lady Macbeth. Initially, when she learns of what the Weird Sisters told him, she believes that he is "too full o' th' milk of human kindness" to take the quickest path to the throne of Scotland: murdering the current king (1.5.17). She indicates her willingness to manipulate her husband so that he does as she would wish, hoping that he comes directly home so that she
may pour [her] spirits in [his] ear
And chastise with the valor of [her] tongue
All that impedes [him] from the golden round (1.5.29–31).
She is quite prepared to persuade and coerce him to kill the king and take the crown, as she anticipates disagreement.
Later, Macbeth determines that he will "proceed no further in this business" of murder (1.7.34), and he tells Lady Macbeth that they are not going ahead with their plan to kill Duncan. She goes on to insult and berate him, claiming that he is not really a man but a coward if he will not go after what he wants. She also suggests that he does not really love her and that his love is weak because he is breaking his word to her. She wounds his pride deeply through their conflict, and as a result, Macbeth does kill Duncan.
Soon, the couple begins to grow apart as Macbeth plans more and more acts of violence without so much as consulting his wife. Perhaps this change in him was precipitated by her treatment of him prior to and following the murder of Duncan. She continued to insult him for being cowardly and weak because he felt so remorseful and fearful about what he'd done. Their conflict helps to convey the theme that appearances are often deceiving. It appears, at first, that Lady Macbeth is the strong one—the one who can hold it all together, even through stressful times—and it likewise seems as though Macbeth is the weak one who will fall apart. However, by the end of the play, we see that Lady Macbeth is the weaker party, the one whose conscience gets to her, and Macbeth is the one who seems most strongly committed to their plan.