how does the banker change from the beginning to the end of the story

The banker learns that his youthful conceit was a futile characteristic. The banker goes through much emotional trauma over this wager. He loses his fortune and then even contemplates killing the lawyer to nullify the bet. Having secretly read the lawyer's letter, the banker realizes the arrogance former self. The banker feels a "a great contempt for himself" for putting the lawyer, a fellow human being, through such an ordeal.