Neither physical deformity nor ambition are beliefs appropriate to his behavior. Only Richard's pleasure and Shakespeare's power differentiate Richard from Macbeth. Macbeth's response to his operation is one of horror. Rabkin raises the question of what motivates Macbeth; the answer lies in Lady Macbeth's explanation for her failure to kill Duncan. He cannot kill Duncan because it would be a form of parricide, and this is precisely why Macbeth is driven to kill. Rabkin makes it clear that this could be a reason, but the reason he acts in that moment is the anger of a disappointed brother; the act of treating Malcolm like a favorite son triggers a murderous impulse. Critics of the time demonstrated how Shakespeare's understanding of character is amenable to psychoanalytic exploration and how Shakespeare appears to have predicted modern psychological discovery. Rabkin claims that what we find in Macbeth is more of a dark hint at motivations that lie buried deep; too deeply to be capable of explanation in the seventeenth century. Macbeth's behavior is simply based on unconscious motivations that he himself is unable to know. Rabkin concludes that human behavior is essentially governed by unknown and unknowable forces from within and without