Lady Macbeth greatly influences her husband to kill King Duncan. Although the witches had planted a seed in Macbeth, he had changed his mind on killing King Duncan. In Act 1, Scene 7, Macbeth tells his wife that they will proceed no further in murdering King Duncan:
We will proceed no further in this business. He [Duncan] has recently honored me...
At this comment, Lady Macbeth is furious. She uses manipulation to control Macbeth. She insults his manhood by asking him if he is afraid to kill King Duncan:
Are you afraid To be the same man in reality
As the one you wish to be? Would you have the crown
Which you believe to be the ornament of life?
Lady Macbeth shames Macbeth by insulting his manhood. She challenges his bravery. She states that Macbeth was a man when he dared to kill King Duncan. This type of manipulation works on Macbeth. Moments after this conversation, Macbeth quotes that he will follow through with King Duncan's murder, claiming that Lady Macbeth has convinced him to commit the murder:
I’m convinced, and I commit
Every part of my body to this terrible event.
Truly, Lady Macbeth is the deciding factor in the murder of King Duncan. She gets what she wants. She is more determined than Macbeth seems to be in the devious plan to murder King Duncan and take his thone.
I think I will have to go with his wife Lady Macbeth on this one. Sure Macbeth is into being king. As soon as the witches start with their "suggestions" the wheels start turning in Macbeth’s little head. Even Banquo notices this in his friend, "Look, how our partner's rapt". This is about the extent of Macbeth's plans to kill Duncan. He flip- flops back and forth, finally deciding to let chance crown him. This resolve lasts for about two minutes when he gets back the old homestead (castle). Lady Macbeth knows how to manipulate her husband. Basically she calls him coward and questions his manhood. Shakespeare's leading men really hated when their manhood was questioned. Macbeth is especially vulnerable to this; outside the battlefield he had some pretty low self-esteem going. The prodding and insults are enough to push Macbeth in the right or wrong direction. L. Macbeth is able to use her husband to orchestrate the rather inept murder of Duncan. Unfortunately for her, the murder is the catalyst to send Macbeth on a one way ticket to paranoid crazy town.