Ambition is a key element of Macbeth and features in any description of Macbeth's own character as his "vaulting ambition"(I.vii.27) overtakes all sense of reason and decency. Macbeth's drive is only equalled and even surpassed by Lady Macbeth's as she is willing to "unsex" (I.v.37) herself if it will further her ambition to crown Macbeth as king. Macbeth is Lady Macbeth's "dearest partner of Greatness"(12) and except in her nurturing toward him, nothing shall "shake my fell purpose"(43) .
Lady Macbeth is required to manage Macbeth's fear, guilt and confusion as he slips between his ambition and his knowledge of good and evil. When he almost decides to "proceed no further in this business"(I.vii.32), Lady Macbeth's ability to manipulate for her own ends convinces Macbeth that he could be "so much more the man."(51)
Macbeth's ambition is all the more intense considering that Banquo was subject to the same apparitions but recognizes "the instruments of darkness"(I.iii.25) and, as much as he is intrigued by the possibility of his sons being kings, he expresses more curiosity than anything. Perhaps it is because of that lack of selfish ambition that he failed to recognize Macbeth's deadly intentions until too late.
The witches ambition should not be overlooked in a description of ambition as they served to further their own "foul" deeds including Macbeth destroying himself as he is "spiteful and wrathful"(III.v.11) Their "charmed" pot serves to inspite them to create and cause "toil and trouble."(IV.i.10)