In Shakespeare's Macbeth, the character of Lady Macbeth illustrates well the "mind over matter" vulnerability. Unlike her husband, who fights in battles and commits or orders several murders, Lady Macbeth is passive in the commitment of these heinous acts. However, she does encourage Macbeth in his murder of the king, Duncan; and, ironically, she berates Macbeth for being weak. In her speech, she seems ruthless and determined:
And fill me, from the crown to the toe, top-fulll
Of direst cruelty! Mke thick my blood,
Stop up th'access and passage to remorse
That no compunctious visiting of nature
Shake my fell purpose, no keep peace tween
Th'effect and it! (I,iv,, )
However, in contrast to the first three acts in which Lady Macbeth appears cold and calculating, her actions in the last two exhibit much less force, confidence, and ambition, pointing to the line from Hamlet's famous "to be, or not to be" soliloquy: "Thus, doth conscience make cowards of us all."
What seems to trigger Lady Macbeth's mental steeliness is the blood of these murders. "This is a sorry sight," Macbeth says after he returns from killing Duncan; Lady Macbeth is for washing the "filthy witness" off, yet this blood as witness of their crimes sticks not just to Macbeth's hands, but to her mind. In Act V, then, it is an altered Lady Macbeth that the reader/audience witnesses. Now she suffers from what the doctor calls "a great perturbation," and becomes obsessed with removing the blood from the steps in the vain hope of alieving her tortured mind/conscience:
Out, damned spot! Out, I say!....Hell is murky. What need we fear who know it, when none can call our pow'r to accompt? Yet who would hav though the old man to have had so much blood in him? (V,i,36-41)
"This disease is beyond my practice" (V,i,60) the doctor tells the gentlewoman. The conscience of Lady Macbeth that she would subdue in both herself and in her husband, has emerged victorious over all else in her nature, costing her her mind.
Indeed, Macbeth follows the "air-drawn dagger," a "false creation," a "dagger of the mind" proceeding from his "heat oppressed brain." And it mashals him the way to dusty death.
At the beginning of the play, Macbeth is a perfect thane, willing to suffer bodily, to the death, for his King. Matters of the body are easier for a thane to discern than are matters of the mind. His body knows when it's being attacked and, with a sword, it can defend itself. But with the mind, it's not so obvious.
After the first battle in Act I, Macbeth suffers a psychological and moral dilemma when the witches, using half-truths (and therefore lies), present him with the idea of becoming king. His mind begins to race, and he writes his wife the news.
Macbeth, unlike Banquo, cannot reconcile truths from lies, so he chooses only what he wants, the ideal (King). He ignores all logic: the part about protecting his King, God's holy vessel, his kinsman (relative), and his guest. Pathos trumps logos: vaulting ambition wins out.
Hearing of Macbeth's dilemma through the letter, Lady Macbeth, who is not used to suffering bodily, casts off her conscience (her Superego), leaving a moral vacuum. She invites "spirits" into her body, the Id to reign. And so, from Act I on, Lady Macbeth becomes a walking, talking overgrown child who selfishly wants and wants and who cannot deal well with suffering of the body or mind. Her sleepwalking, mental illness, and suicide are all signs of an irreconcilable division between body and mind and of an Id out of control.
Macbeth too relies too heavily on his Id. In Act III, he goes on a killing spree, murdering his best friend, women, and children--all because he is paranoid of losing the crown. By Act V, he is so Id-driven that he thinks he is invincible. He realizes he has lost all reason and compassion, but it's too late. Ironically, he loses his head for it--a division of the body and mind forever.