In "The Bet," why does the narrator call the bet "wild" and "senseless"?

     "Agreed! You stake your millions and I stake my freedom!" said the young man.

     And this wild, senseless bet was carried out!

Anton Chekhov had an idea he wanted to develop into a short story. A man bets another that he can spend fifteen years in solitary confinement. He will receive a fortune if he can do it. Chekhov's biggest problem was "selling" this concept to the reader. Would anyone really make such a bet? Would anyone agree to spend fifteen years in solitary confinement? And, if so, would anyone agree to pay him two million rubles for doing so?

All of the opening exposition is presented as a flashback in the banker's mind as he is remembering how the bet came to be made. This is all mainly to persuade the reader that it was not only possible but that it was actually carried out. The words "wild" and "senseless" can be understood to be part of the banker's recollection and not of the anonymous narrator. What Chekhov is doing is convincing the reader that the preposterous bet was really made by having the viewpoint character himself admit that it was "wild" and "senseless." The banker agrees with the feelings of the reader. This is not the only place in the story where the banker agrees with the reader that the bet was improbable, bizarre, dangerous, perhaps even illegal. Here is another place:

"What was the object of that bet? What is the good of that man's losing fifteen years of his life and my throwing away two million? Can it prove that the death penalty is better or worse than imprisonment for life? No, no. It was all nonsensical and meaningless."

The reader can't argue with the banker because the banker agrees with him. It was all nonsensical and meaningless; nevertheless, it was carried out. Chekhov wanted to write the story, and so he used all his powers to persuade the reader that it really happened. Once the term of imprisonment begins, the reader accepts it as a fait accompli. Chekhov tries in various ways to ameliorate the prisoner's suffering. He lives in a comfortable guest lodge. His meals are brought to him, and they are probably the same as the banker himself eats. He can have wine with meals if he so desires. Best of all, he can have books, music, and virtually anything else he wants except human contact. There is also the fact that the prisoner may walk out a free man any time he chooses, if he forfeits the bet.

Chekhov specifies that the bet was made at an all-male party. We know there must have been a lot of drinking being done--vodka, champagne, brandy, etc. But Chekhov doesn't say a word about liquor. He doesn't want to suggest that the banker and lawyer made the bet because they were both drunk. That would invalidate the bet. But it seems highly likely that both men were drunk when they made it and then didn't know how to call it off when they were sober. The banker subsequently tries to get the lawyer to back out, but the lawyer is young and greedy; he wants those two million rubles.

The bet really is wild and senseless, but Chekhov sold his premise to the reader and made one of his best stories out of it.