When I asked my students for examples of diminishing marginal utility, one wiseguy freshman stated, “Time with my girlfriends after a relationship of five months-I drop them after that.” (I should have told him that it’s hard to distinguish quits from layoffs, but I wasn’t fast enough on my feet!)
His example got a good laugh, but it also allowed me to introduce the notion of addiction, my next lecture topic. How can we explain addiction, in his case the fact that he went out with another girlfriend, and probably even liked her more initially than the first girlfriend? I assume that he had become addicted to falling in love, not staying in love, so that he enjoyed the first few dates with the next girlfriend even more than those with the dumped girlfriend. After a while, however, the marginal utility of his time with her diminished, and their relationship ended too.