In "Macbeth," Lady Macbeth says of human nature, "It is too full." How thoroughly does she understand her husband's or her own?
In Act I, Scene 5, Lady Macbeth has just received a letter from Macbeth imparting the news of his meeting with the Weird Sisters and their predictions. Then he tells her in the letter about the messenger informing him that one of their predictions has already occurred with his new title, Thane of Cawdor, and that there is yet another prediction, to become King. He calls her, "My dearest partner of greatness." Lady Macbeth understands her husband's nature all too well at the onset of the play. He hesitates in killing Duncan and is overcome with guilt; his nature does consist "o' th' milk of human kindness." However, she underestimates his strength and his vaulting ambition in this speech: "Thou wouldst be great, art not without ambition but without the illness should attend it." As the play progresses, his ambition, most certainly, is accompanied by the illness which Lady Macbeth thinks he lacks. Macbeth's ambition is a malady; he destroys everyone in his path on his journey to his own self-destruction. Lady Macbeth does not know the depths of her husband's ambition or his capacity for evil. Neither does she realize her own vulnerabilty and weakness of spirit that will lead to her suicide!