Macbeth and Lady Macbeth complement one another perfectly. Macbeth and Lady Macbeth are both ambitious, but Lady Macbeth is more of a planner. Macbeth wants things, but does not want to work for them. Lady Macbeth is willing to do the thinking and preparation, but she does not want to actually carry out the deed. For that she needs Macbeth.
Lady Macbeth immediately gets to work when she hears of the prophecies. She is ready to make her husband king. The only thing that stands in the way is his kindness and his cowardice, according to her. She believes she can work on him and get him to see her way.
Hie thee hither,
That I may pour my spirits in thine ear,
And chastise with the valor of my tongue
All that impedes thee from the golden round,(25)
Which fate and metaphysical aid doth seem
To have thee crown'd withal. (Act 1, Scene 5, p. 90)
Lady Macbeth understands that she herself does not have the guts to kill Ducan (and perhaps the strength), but her husband won’t act unless he is spurred on. She becomes the thorn in his side, pushing him to act. She plans everything and sets him in motion. She makes sure the plan is carried out.
It turns out that when pushed Macbeth becomes quite violent. Once he starts killing, he seems unable to stop.