Ambition is one of the qualities expressed by Lady Macbeth when she is first introduced in the play. Ambition is a part of human nature and being ambitious can be defined as being 'eager for success'. After Lady Macbeth reads the letter from Macbeth, she was ambitious for Macbeth, her husband, to become everything that he can be, while she was also aware of the "illness" that should attend ambition.
"Glamis thou art, and Cawdor, and shalt be
What thou art promised; yet I do fear thy nature,
It is too full o'th'milk of human kindness...
Hie thee hither,
That I may pour my spirits in thine ear
And chastise with the valour of my tongue..."
This can appear as ruthless and evil, yet it also shows Lady Macbeth's loyalty and love for Macbeth. Just as Macbeth is ambitious for the throne, Lady Macbeth is driven to assist him and for this reason, Lady Macbeth cannot be considered pure evil.
One of the ways Lady Macbeth chooses to achieve her ambition is through manipulation. Lady Macbeth herself is the driving force behind Macbeth's actions. She manipulates Macbeth with remarkable effectiveness and overrode all the objections of his conscience. She uses blackmail and repeatedly questions his manhood until he feels that he must commit the murder of Duncan to prove himself:
"...From this time,
Such I account thy love. Art thou afeard
To be the same in thine own act and valour
As thou art in desire? Would'st thou