Macbeth is aware of how ambitious he is. He recognizes that he should appreciate the honors bestowed upon him by King Duncan. He tells Lady Macbeth that they will proceed no further in the business of murdering King Duncan. He has a made-up mind:
We will proceed no further in this business.
He has recently honored me, and I now have the
Golden opinions from all sorts of people,
Which I want to enjoy for a bit longer, and
Not cast them aside so soon.
Macbeth would have been content to bask in the honors bestowed upon him. He would have been satisfied being Thane of Cawdor. He had put aside thoughts of murdering King Duncan. He is matter of fact in his decision, but Lady Macbeth has other plans. She is the ambitious one. She is determined that Macbeth will become king of Scotland.
Lady Macbeth uses manipulation to get what she wants. She challenges Macbeth's manhood. She uses manipulation and control to persuade Macbeth to follow through with the murdering of King Duncan.
Macbeth had decided to bask in the honors bestowed on him. He had decided to give up the notion of murdering King Duncan. It was Lady Macbeth's ambition that leads Macbeth into murdering King Duncan.
Truly, Macbeth is aware that he has become overly ambitious. He thinks things through and decides they will not proceed any further in the business of becoming murderers of King Duncan. Lady Macbeth becomes Macbeth's motivation. She convinces him that he is to act like a man and take the throne form 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,
And yet live like a coward in your own self-esteem,
Through manipulation, Lady Macbeth persuades Macbeth to act upon his earlier desires to have the throne. Macbeth replies that he is convinced by Lady Macbeth's bidding:
I’m convinced, and I commit
Every part of my body to this terrible event.
Macbeth gives in to what he calls a "terrible event." He knows that it is not the right thing to do, but his Lady is very convincing. While Macbeth had changed his mind, Lady Macbeth convinces him otherwise. No doubt, Lady Macbeth is the ambitious one. Macbeth just wants to please Lady Macbeth.