Characters struggle, and in some cases, suffer with the aftermath of decisions they or others have made. Please read the details!
Identify and explore the characters that seem to be the best examples available in Macbeth and Frankenstein
Victor's decision to destroy the partner he was creating for the Creature is the one decision that determines everything that happens to him for the rest of his life. If he had just created the partner, the creature and his mate may have left for the mountains and never been seen again. Victor could have married Elizabeth and lived his own "happily ever after" life. Of course, if this had happened, we would have had a different book. But Victor's decision is very strange. He claims that he did not want to create a race of "monsters" that could terrorize mankind; but how difficult would it have been to create a female without reproductive capabilities? It seems hard to believe that he didn't think of this; on the other hand, in a book where a being is created from oversized spare parts from a wide variety of sources gathered over a long period of time, there may be nothing that is hard to believe.
I agree with the above post, and would add that the creation of the monster is the act which brings the most suffering for Victor Frankenstein. The deaths of William and Justine are the direct results of his decisions, and he is wracked by the guilt of these crimes throughout the rest of the novel.
Even the monster himself is forced to deal with suffering and isolation as a result of his actions. His desire to find a place within society drives him toward human contact, yet his seemingly uncontrollable need for revenge drives him further away. Indeed, he must struggle with the consequences of every action, as his very existence brings him pain. He will foreve rbe "the Other", and every moment of life brings suffering. And of course, all of this is again the result of Victor's decision to create him in the first place.
As for Macbeth, look to Lady Macbeth. Her goading of her husband and his murder of Duncan leads directly to her breakdown. She suffers as a result of both her own actions and her husband's.