When the lawyer and the banker make the bet, both have enough financial stability to wager two million rubles without a moment's hesitation. They rush into this bet in an effort to validate their own opinions about capital punishment.
Over the next fifteen years, the lawyer changes dramatically, undergoing deep internal changes as a result of his confinement. Unknown to him, the banker loses his wealth during that same time period, and when the fifteen years are almost over, he really can't afford to pay the lawyer. He therefore plots to sneak into the lawyer's chamber and kill him.
He finds that the lawyer has written a note and plans to leave minutes before the fifteen years are over, thereby forfeiting his two millions. He has transformed into a man who rejects the values of society. He despises "worldly blessings" and sees the world as "delusive." He believes that humanity is "proud and wise" and that the world has gone "mad." He insists that humans proclaim "falsehood for truth."
After reading these words, the banker is filled with self-contempt because he recognizes himself in the words of the lawyer's claims. He values this man's life so little that he is willing to kill him in order to keep his own two million rubles; this is exactly the madness which the lawyer speaks of. The banker has spent a lifetime chasing the monetary values of a world which has ultimately left him with as much debt as wealth. He has deluded himself into thinking that the quest for money would bring him happiness and finds that he is miserable after spending a lifetime nearly solely focused on this goal.
The banker's contempt toward himself signifies that he sees the great and painful truth in the lawyer's words.