Let's say that a man was living comfortably off of $150,000 a year, but now he is making $250,000 a year. The question is, what will happen to the man's behavior when he is off work? Since the opportunity cost of not working is higher, will the man relax less? However, if the man is making more than enough money for himself, will he use his extra capital to hire a janitor to clean his house for him (assuming that he still has plenty of money left over to save millions for his retirement), thus increasing the amount of time he lounges around?
Very good example of increased productivity leading to an increase in the opportunity cost of leisure. This is also a good example of decreasing marginal benefits. When the man was spending his first $150,000 a year, he was putting it into things he valued more. As his salary increased, things he valued less became attractive to spend those marginal dollars on.