B: the desire to prove to others that you’re right can lead to extreme actions.
In the story, the lawyer and the banker get into an argument about whether or not life imprisonment would be more humane than capital punishment. The banker challenges the lawyer to a bet stating that the lawyer must remain in isolation for 15 years. To prove that he is right, the lawyer takes the bet. The desire to prove himself correct leads the lawyer to take the extreme action of giving up everything and living a life locked up in solitude.