What evidence is there that Lady Macbeth is not as strong as she would like to believe in Shakespeare's Macbeth?
In Shakespeare's Macbeth, Lady Macbeth, particularly in the first two acts of the play, comes off as or appears to be very strong. She is obsessed with power and extremely aggressive, especially for a female in both Shakespeare's time (when the play was written) and 11th century Scotland (when and where the play is set). She totally commits herself to the assassination of Duncan and even manipulates her husband to convince him to go through with it.
Lady Macbeth appears to be strong and ruthless when she prays to her spirits to be made more like a ruthless warrior, for instance. She wants no trace of womanish or mother-like pity to enter her mind when the time comes to kill Duncan. Later, when convincing her husband to go ahead with the killing, she declares she would rip a baby from her breast and smash it against rock if she were to change her mind about something as Macbeth has changed his mind about the assassination.
Yet, the play reveals not only that Lady Macbeth is not as strong as she appears to be, but also that she, herself, has doubts about her own strength, as she defines it.
First, the fact that she prays to be made more pitiless and ruthless reveals that she is worried about how pitiless and ruthless she really is. If she is really as bad as she appears to be, why does she have to pray to be changed?
Second, she can't quite bring herself to kill Duncan out of sentimentality. She can't do it because the sleeping Duncan reminds her of her father. Certainly, this places her as a traditional, stereotypical female/loving daughter, not as a ruthless warrior.
Finally, Lady Macbeth cannot mentally handle what her original intention leads to. She never planned for Banquo and Macduff's family to be killed. When she experiences what her husband turns into, she suffers a mental breakdown. To the audience, that makes her more human. According to her own views expressed in the first two acts of the drama, however, that makes her weak.
Lady Macbeth fulfills her role among the nobility and is well respected like Macbeth. King Duncan calls her "our honored hostess." She is loving to her husband but at the same time very ambitious, as shown by her immediate determination for Macbeth to be king. This outcome will benefit her and her husband equally. She immediately concludes that "the fastest way" for Macbeth to become king is by murdering King Duncan.
The almost superhuman strength Lady Macbeth rallies for the occasion and her artful and sly ability are shown through her meticulous attention to detail regarding the murder. When Macbeth returns to their chamber she goes back to the murder scene and cleverly smears the grooms with Duncan's blood. However, her morals had prevailed just a while before as revealed through her comment that she would have killed Duncan herself had he not "resembled [her] father as he slept."
Perhaps Lady Macbeth felt that suppressing her conscience for the deed was enough and that later the thought of the deed would just dissipate. The outcome is not this way, though, because Macbeth and Lady Macbeth often cannot go to sleep, and if they do, they experience terrifying dreams. But still, Lady Macbeth is able to maintain her sanity and composure during the day, even more than her husband. She urges him to be light hearted and merry. Once she practically rescues Macbeth from the frailty of his own conscience. When Macbeth sees Banquo's ghost she creates an excuse to explain his odd behavior. She attempts to chasten Macbeth by again questioning his manhood. When the situation grows worse though, she takes charge once more and promptly dismisses the lords from the feast.
Later, though, the burden of Lady Macbeth's conscience becomes too great for her and her mental and physical condition deteriorates. A gentlewoman observes her sleepwalking and consults a doctor. The doctor and the lady observe Lady Macbeth sleepwalking, madly trying to cleanse her hands of the blood of Duncan and Macduff's family. Still in her sleep, Lady Macbeth asks, "what, will these hands ne're be clean?" foreseeing that she will never have peace of mind. She also retells events of the day Duncan was murdered. The doctor tells the gentlewoman that what Lady Macbeth needs is spiritual and not physical help.
Lady Macbeth's condition worsens, and she goes in and out of sleep with delirious visions. Macbeth asks the doctor to cure her or give her a drug that will erase the troubles of the heart. The doctor responds that he cures physical not moral problems. Later, as the battle ensues outside of Dunsinane, by unspecified means Lady Macbeth commits suicide.
At the beginning Lady Macbeth finds strength to entice Macbeth to murder Duncan and to follow through with the murder herself. As time advances though, her pretended strength diminishes as she fights the torments of her conscience. Tending to her conscience engulfs and destabilizes her so that she can not support Macbeth against Malcolm. Lady Macbeth's attempts to suppress her conscience fail. At the end she chooses death because she can no longer bear the torments of her guilt.
To quote Bradley, ‘Lady Macbeth is perhaps the most awe- inspiring figure that Shakespeare ever drew. Sharing certain traits with her husband, she is at once clearly distinguised from him by an inflexibility of will, which appears to hold imagination, feeling and conscience completely in check.