Lady Macbeth and Victor Frankenstein both regret their actions. Each creates a different kind of monster, and then feels remorse and self-pity.
Lady Macbeth is mad with glee in Act 1 when she decides to spur her husband on to kill Duncan. At this point, she is not thinking about the consequences. In scenes 5 and 7, she is only interested in results. She wants what she wants, and she encourages and pushes him past all reluctance until he finally gives in.
I … know
How tender ’tis to love the babe that milks me:
I would, while it was smiling in my face,…
And dash'd the brains out… (Act 1, Scene 7)
At this point, she is pleased with her violence and mischief, and encourages her husband to be as violent as she is. However, she soon finds that she cannot stop what she has started. She regrets having turned her husband into a homicidal monster.
Out, damned spot! Out, I say! …
Yet who would
have thought the old man to have had so much blood in(35)
him? (Act 5, Scene 1)
Lady Macbeth has basically lost her mind because facing the reality of what she has done is too painful. She would rather die because she realizes the part that she has played, and she is overwhelmed with guilt.
Victor Frankenstein is also quite ambitious. He wants what he wants, and no one is going to tell him differently. He finds a way to create life from where there was none, so he builds the creature even though it is against the laws of nature. However, unlike Lady Macbeth he seems to pause before actually acting on his ambitions.
When I found so astonishing a power placed within my hands, I hesitated a long time concerning the manner in which I should employ it. (ch 4, p. 26)
Victor does build the creature though, and when he does his reaction is much the same as Lady Macbeth’s reaction to her husband the murderer. He is full of regret, shame, and fear.
I passed the night wretchedly. .... Mingled with this horror, I felt the bitterness of disappointment. (ch 5, p. 29)
Victor’s creation ultimately destroys him too, although it takes some time before the full effects really hit home, as in Lady Macbeth’s case.
Lady Macbeth and Frankenstein both act on ambition without paying attention to the consequences, and both pay the price. They regret their creations, and blame themselves for the destruction they cause.