The Bet" is a bizarre story, and one that is unusual for Chekhov. Everything about the story is strange and hard to believe. Would anyone be crazy enough to make a bet like that? Would any rich man be crazy enough to harbor a prisoner for such a length of time? The ending is no more bizarre than the rest of the story. The rich man over time has lost much of his wealth and cannot pay off on the bet, so he decides to kill his prisoner. In the meantime, the prisoner has learned so much in studying history, literature, philosophy, and other subjects that he no longer cares about money. It is truly a fantastic story and deserves a fantastic conclusion. Chekhov usually wrote much more realistic stories with inconclusive endings, such as in "The Lady with the Little Dog." In "The Bet," Chekhov seems to be showing what he could do in more imaginative fiction if he wanted to. He seems to be emulating Edgar Allan Poe. Chekhov does a marvelous job of representing the long passage of time in a short story.
Its not the answer.We see that in the middle of 15 years imprisionment he has been realizing what exactly life is,and at the end he became as wise as he would teach the banker that the life is worth nothing.