10. Why does the banker lock up the prisoner’s letter in a fireproof safe?

Even though the banker does not want to pay the money, he does not want people to see the note. He does not want people to see that the money would not have been paid; the man imprisoned for fifteen years had moved beyond the superficial nature of the bet. The "compact" is broken, but the man wants to seem the "better" of the two. He does not want what the man has learned to be revealed to the rest of the population.

And, by the way, this story is by Anton Chekhov.