After initially deciding to kill Duncan so that he can become king, Macbeth changes his mind, as he cannot find a legitimate reason for this (other than his own personal gain). Lady Macbeth does three specific things to get her husband to go through with the murder as promised. First, she plays into his pride and honor as a man. Then, after she has gotten him into the right mindset, she tells him her plan to frame Duncan's chamberlains. Finally, to erase the Macbeth's remaining doubts, she tells him that if they act surprised, grieved, and upset, nobody will question their innocence.
After Macbeth has decided not to kill Duncan, his wife berates him. She plays into his pride by attacking his courage, manhood, and commitment:
Art thou afeard
To be the same in thine own act and valour
As thou art in desire? Wouldst thou have that
Which thou esteem'st the ornament of life,
And live a coward in thine own esteem,
Letting 'I dare not' wait upon 'I would,'
Like the poor cat i' the adage?
Here, Lady Macbeth attempts to get Macbeth to act on his desires. She does not outright call him a coward; rather, she leads him away from his fears by framing her argument as a question of whether he will view himself as a coward. This method of reverse psychology works, as he quickly responds, "I dare do all that may become a man; / Who dares do more is none." Macbeth is now in the right mindset for Lady Macbeth to switch gears and alleviate any lingering doubt about the potential success of her plan:
When Duncan is asleep—
Whereto the rather shall his day's hard journey
Soundly invite him—his two chamberlains
Will I with wine and wassail so convince
That memory, the warder of the brain,
Shall be a fume, and the receipt of reason
A limbeck only: when in swinish sleep
Their drenched natures lie as in a death,
What cannot you and I perform upon
The unguarded Duncan? What not put upon
His spongy officers, who shall bear the guilt
of our great quell?
Lady Macbeth's plan—or rather, the way she explains it—appears foolproof. While Macbeth is murdering Duncan, she will get his chamberlains drunk to the point of passing out. Then, she will frame them for his death. After this speech, Macbeth questions an aspect of her plan, but he does not seem to doubt that it will work. She responds that if they play it right, nobody will suspect them: "Who dares receive it other, / As we shall make our griefs and clamour roar / Upon his death?"