Herewith a relatively trivial but, I hope, fun application of marginal thinking. Actually two applications: a subtler one by my non-economist wife (who has lived with an economist for 37 years) and an obvious one by me.

Most Saturdays my wife and I go out to a nice lunch. A couple of Saturdays ago, she wasn’t feeling well and didn’t want to go out. So we agreed that I would get takeout and bring it home. But where to go? I suggested some of our standard places that cost us between $35 and $50, not including tip. Here came her marginal insight: She nixed those places because it didn’t make sense to her to spend that kind of money when, with her stomach feeling the way it was, she wouldn’t get much value out of it. So she suggested Subway.

I went to Subway and noticed that the 6-inch sandwich I like went for $5.99 and the 12-inch went for, if I recall correctly, $7.49. So the incremental cost of the extra 6 inches was only $1.50 plus tax, which totaled about $1.64. It was easy to figure that the value of that extra 6 inches, for breakfast or lunch the next day, was well above $1.64. So I bought the 12 inch and, sure enough, had a delicious lunch the next day as well.

Culinary note: Some people don’t like a Subway sandwich the next day, especially if they get mayo and mustard, as I do, because the sauces seep into the bread, making it gooey. I love that. When my sister and I took a bus from Winnipeg down to Nacogdoches, Texas in April 1965, my aunt whom we visited packed tuna fish sandwiches for the return trip. Unaware of the danger of leaving mayo at room temperature, I didn’t finish the last one until over half way through the 50-hour bus ride, I think somewhere in Iowa. It was yummy.