Since the story is told entirely from the banker's point of view, both in the present and in flashbacks, the problem must be his. Obviously, the lawyer has a big problem keeping his mind occupied for fifteen years while remaining in solitary confinement; but the fact that the prisoner actually does manage to stick it out for all those years makes the banker's problem more and more serious.
When the story opens the banker's problem has reached the critical stage. The first part of the story is taken up with flashbacks telling how the bet originated and how the prisoner has apparently been existing in his confinement. The banker made the bet in complete confidence because he was positive that the young lawyer could not endure solitary confinement for more than a few years at most, and that he would voluntary forfeit the bet by breaking the seal on the door, as he was free to do at any time, and walking out of the lodge.
The old man remembered all this, and thought:
"To-morrow at twelve o'clock he will regain his freedom. By our agreement I ought to pay him two million. If I do pay him, it is all over with me: I shall be utterly ruined."
This quote expresses the story's problem succinctly. The banker is appalled at the tenacity of his prisoner. The young lawyer has been making the best of his captivity for fifteen years. He has read over six hundred of the world's best books in many different languages which he taught himself to understand. He has not been able to see or talk to any human being, but he has had a comfortable life at the banker's expense. He can even have wine with his meals. He is not like the Count of Monte Cristo but more like a gentleman of leisure. Meanwhile the banker has been growing older and losing his self-assurance along with a lot of his money.
Fifteen years before, his millions had been beyond his reckoning; now he was afraid to ask himself which were greater, his debts or his assets.
The banker's problem is that if he pays the prisoner two million rubles he will be bankrupt. His estate will be confiscated. He will have nothing to live on. His only solution to this terrible problem is to murder the prisoner before twelve o'clock noon tomorrow. An alternative would be simply to refuse to pay the debt. This, of course, would be disgraceful and dastardly after keeping a man imprisoned for fifteen years.
Chekhov was clever in designating the young man as a lawyer, because he would have realized even when he first made the bet that he could have legal recourse if the banker defaulted. If the banker refused to pay voluntarily, the court would award it to the prisoner anyway. There could be no denying that the agreement was made, because Chekhov specifies that it was made in front of a large assembly of men at a party. And there could be no denying that the lawyer had been kept prisoner for fifteen years in accordance with the agreement.
The story has a surprise ending. The prisoner voluntarily defaults by leaving before the deadline. The banker is seriously considering committing a murder to save his fortune, but he has not definitely decided to do it. Chances are that he would have gone through with the crime by suffocating the weakened prisoner with a pillow.
At no other time, even when he had lost heavily on the Stock Exchange, had he felt so great a contempt for himself. When he got home he lay on his bed, but his tears and emotion kept him for hours from sleeping.
in the story of the bet by anton chekhov