One chief literary element that is used by Chekhov in this excellent and profound short story is comparison of the banker's emotions with his actions, and how the discrepancy between the two reveals the banker's materialism and lack of willingness to change and learn from his experience. Note how, after reading the note that the man who agreed to live in solitary confinement for fifteen years, the banker is affected very strongly:
When the banker had read this he laid the page on the table, kissed the strange man on the head, and went out of the lodge, weeping. 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.
This rather extreme emotional reaction suggests the banker has learnt an important lesson about himself and his attachment to material possessions, which of course the man who wrote the note has just ultimately rejected with his intention to default on the terms of the bet. The use of the word "contempt" is very strong and likewise implies the banker has been forced to take a long, hard look at himself, and his sleepless night suggests that he is thinking of how he will change as a result. However, after the man has defaulted on the terms of the bet, the very next paragraph "locked [the letter] up in a fireproof safe" to make sure that he has the rejection of the money recorded and safe. This action, juxtaposed to his earlier emotional response, reveals a central discrepancy in the banker's character. Although he was certainly struck by the man's rejection of material possessions, he has not acted on that in any way, as he only acts to preserve his belongings and wealth. Juxtaposition is therefore a key literary technique that is used to expose the true attitudes and feelings of the banker and reveal one of the central themes of this story.