A similar theme in both stories is the influence of decisions on character, or who a person becomes.
Macbeth chooses to follow his wife’s advice and kill King Duncan. As a result, he deteriorates from a loyal and valiant solider to a paranoid tyrant. Malcolm reminds Macduff that he used to regard Macbeth as a friend, and many others considered him a good person.
This tyrant, whose sole name blisters our tongues,
Was once thought honest. You have loved him well;(15)
He hath not touch'd you yet. (Act 4, Scene 3)
Macbeth does touch Macduff, killing his wife and son, as well as others in the household. Macbeth does not benefit from this murder, and instead goes deeper and deeper into a downward spiral of murder and madness, relying more and more on the witches’ prophecies to make his decisions, eventually succumbing to Macduff in battle.
Ambition and jealousy also mar Gene’s relationship with his roommate Finney. Gene is jealous of Finney, and when he accidentally/on purpose knocks him off a tree branch, destroying his athletic ability, he has to live with the consequences. The knowledge that he destroyed his friend’s life slowly eats away at him.
It struck me then that I was injuring him again. It occurred to me that this could be an even deeper injury than what I had done before. I would have to back out of it, I would have to disown it (ch 5)
Gene can’t admit that he did what he did on purpose, even to himself. It influences the way he sees himself, and the way he develops as a boy—as well as the person he becomes.
In each case, one event—Macbeth’s murder of Duncan and Gene’s betrayal of Phinney—has such an effect on the development of character for the person that everything else that happens afterward is an outgrowth of that event, and the character is another person.