How does the lawyer's behavior change from year to year during imprisonment?

I am fairly certain that this question is asking about Anton Chekhov's short story "The Bet." The lawyer in the story does indeed change over the course of his 15 years in "prison." When readers are first introduced to him, he is full of confidence in his own abilities and in his thoughts about capital punishment.

Capital punishment and life-imprisonment are equally immoral; but if I were offered the choice between them, I would certainly choose the second. It's better to live somehow than not to live at all.

He is so confident in his opinion and in his ability to stay in prison that he ups the bet from five years to fifteen. Why he does not ask for more money as well is beyond me. Perhaps it is because he believes that a payment of two million is enough to begin with. It is hard to say because the story does not give readers any insight into the lawyer's thoughts. I believe that a reader can confidently say that the money is somewhat important to the lawyer at the beginning of the story. That is part of the reason to take the bet in the first place. By the time the fifteen years are over, though, the lawyer wants nothing to do with the money. He has gained tremendous amounts of wisdom and insight into the world through all of his reading.

Your books gave me wisdom. All that unwearying human thought created in the centuries is compressed to a little lump in my skull. I know that I am cleverer than you all.

A result of all of his newfound knowledge and wisdom is the lawyer's general disgust for mankind's love for money and material things. He sees it all as meaningless.

Everything is void, frail, visionary and delusive as a mirage. Though you be proud and wise and beautiful, yet will death wipe you from the face of the earth like the mice underground; and your posterity, your history, and the immortality of your men of genius will be as frozen slag, burnt down together with the terrestrial globe.

He is so confident in his opinion that he intentionally loses the bet. He no longer wants the money.

That I may show you in deed my contempt for that by which you live, I waive the two millions of which I once dreamed as of paradise, and which I now despise.

The lawyer has been transformed from a man that had hope in mankind and desired money to a man that eschews wealth and mankind entirely.