Final answer:
Lady Macbeth's decision shows her manipulative yet emotionally limited nature, highlighting the conflict between ambition and morality, and revealing her reliance on Macbeth to execute their plan.
Step-by-step explanation:
Lady Macbeth's decision not to kill Duncan herself reveals several complex facets of her character. Firstly, it shows that she is not as ruthless as she would like to think; the resemblance of Duncan to her own father while he sleeps evokes enough humanity in her to prevent her from committing regicide herself.
Moreover, this moment demonstrates the dichotomy between her ambitious plotting and the reality of action, illustrating a conflict between her manipulative nature and her actual capacity for violence. It also highlights her reliance on Macbeth to fulfill their shared ambition, manipulating his sense of masculinity and fiercely challenging his courage to force his hand in the murder.
Throughout the play, she oscillates between being a driving force behind the plot and exhibiting moments of vulnerability, indicating a complex personality driven by forceful ambition yet bounded by her own emotional limitations. Lady Macbeth exerts power over Macbeth, pushing him to commit the deeds that she cannot bring herself to do, which ultimately leads to their mutual downfall.