Throughout the first four acts of Shakespeare's Macbeth, Lady Macbeth is portrayed as a ruthless character willing to do anything to obtain power. Although she occasionally shows some signs of wavering, she seems to remain mentally stable and satisfied with her husband's actions, thus serving as a foil to a guilt-ridden Macbeth. However, in Act 5, Lady Macbeth is suddenly overcome with guilt over Macbeth's behavior whereas Macbeth becomes consumed by his desperate chase for power. This development in Lady Macbeth may seem sudden, but, in fact, it has been building slowly since Macbeth made the decision to kill Banquo. As Macbeth's character goes through a dramatic transformation, Lady Macbeth also changes, foiling his character. Ultimately, she is overcome by regret not only for the murders committed by Macbeth, but also by the fact that she caused Macbeth's drastic character change that cannot be undone. This regret eventually leads to her suicide.
When Macbeth first consults the witches, they inform him that he will one day become king. Macbeth is unsure of what to do with this news, and immediately pens a letter to his wife asking what his next step should be. The idea of killing Duncan had planted seeds in Macbeth's head, but it blossoms once it reaches Lady Macbeth's mind. Lady Macbeth springs into action saying Macbeth "shalt be what thou art promised" (I.V.15-16) despite fearing that Macbeth is "too full o' th' milk of human kindness" (I.V.17). Macbeth is "not without ambition, but without the illness should attend it" (I.V.19-20), or the audacity to do whatever is necessary to become king by killing Duncan. Lady Macbeth is aware of this facet of Macbeth's personality and decides to take matters into her own hands. She realizes that she must be the devil in the back of Macbeth's mind, pushing him towards the glory of ruling Scotland. When Macbeth decides to "proceed no further in this business" (I.