Nothing in marriage demonstrates the law of diminishing returns more than sex. Back when you were single and you weren’t getting any, you really wanted it–and so when you did get it, boy were you happy. You probably worked pretty hard to get it again the next night, didn’t you?
Then you met the love of your life. You had a honeymoon period, during which you had sex all the time.
Eventually, you got married and could (ostensibly) have it any time you wanted it. Yet you no longer wanted it quite so much. Sad.
This is what economists call the law of diminishing returns: the more you have of something, the less it’s worth to you. We call it the plague of diminishing orgasms.