There is no more appropriate title than "The Bet" for Chekhov's story because the bet, or wager, between the young man and the banker is central to the plot as well as to the psychological changes in the characters. In effect, the bet is both the cause and the result of what occurs with the main characters; moreover, this wager between the two men even involves the readers in their predictions, or "betting on" what the outcome of the story will be.
The act of betting is one that involves much of the psychological state of those who wager, their initial viewpoints, and the subsequent development of their states of mind. With respect to the young lawyer, his impulsiveness drives him to make the initial wager with the banker, and his egotism and rash youth cause him to "up the bet" to fifteen rather than five years, perhaps believing that the banker will not take this bet. However, the banker, equally confident, does accept the wager. Then, during this extensive period of fifteen years' confinement, the young man moves from self-indulgence to disciplined study as he matures, but regresses to escape as he is overcome by a factor upon which he has not figured--loneliness and alienation and their consequent hopelessness. These mental and emotional changes are not unlike the various mental states that one who bets goes through--although much more swiftly--as, for instance, he watches a horse race, a fight, or plays a card game in which he begins to anticipate his losses.
As the banker, who is the more passive participant in the wager, watches the lawyer survive his confinement, he, too, moves from confidence to despair, an inner death-in-life not unlike that of the younger man. In effect, the bet has endangered the sanity of both the men. For, while the lawyer writes
"I despise freedom and life and health and all that in your books is called the good thing of the world,"
the banker is dominated by the selfish urge to protect himself financially and contemplates murder when he discovers the lawyer asleep and "half-dead" from his despair. Thus, both men have, in the lawyer's words, "exchang[ed] heaven for earth" in the quick, impulsive act of making a bet.