Quote 1
LADY MACBETH
[…]
Glamis thou art, and Cawdor, and shalt be
What thou art promised. Yet do I fear thy nature;
It is too full o' th' milk of human kindness
To catch the nearest way. Thou wouldst be great,
Art not without ambition, but without
The illness should attend it. (1.5.15-20)
Here's another count against ambition: After reading the letter from her husband (which recounts the witches' prophesy), Lady Macbeth's thoughts immediately turn to murder. Problem: Macbeth has ambition, but he doesn’t have the nerve to see it through. Luckily Lady Macbeth is man enough for both of them.
Quote 2
LADY MACBETH
Your face, my Thane, is as a book where men
May read strange matters. To beguile the time,
Look like the time; bear welcome in your eye,
Your hand, your tongue; look like th' innocent
flower,
But be the serpent under't. (1.5.73-78)
Whenever flowers and serpents come into it, we're ready to suspect Eve and that pesky snake. And sure enough, here's a woman convincing a man to share in her own, nasty little vision of the way things should be.
Quote 3
LADY MACBETH
O, proper stuff!
This is the very painting of your fear.
This is the air-drawn dagger which you said
Led you to Duncan. O, these flaws and starts,
Impostors to true fear, would well become
A woman's story at a winter's fire,
Authorized by her grandam. Shame itself!
Why do you make such faces? When all's done,
You look but on a stool. (3.4.73-81)
Okay, Lady Macbeth. It's easy to make fun of your poor husband when he's the one having the visions. You won't be laughing as hard when you're the one trying wash an invisible bloodstain out of your hand.