(Jerry) Pournelle got back to his seminar, and Heinlein began making notes on his new book. In the course of that evening, Pournelle had casually used an expression they had never heard before: TANSTAAFL. It was an acronym, Pournelle explained, that he got from his father, for the expression, still widely used in the American South (Pournelle had been born in Shreveport, Louisiana, in 1933):

There Ain’t No Such Thing As A Free Lunch. Saloons used to advertise free lunches with drinks—anything from pickled eggs to elaborate buffet spreads. Of course, there was nothing “free” about the food. The cost was folded into the price of the drinks. Free lunches had disappeared from the American scene around the time of World War I. The acronym, collapsing the whole thing into a single word, was exactly what Robert had been looking for:

“I was working on a novel into which it fitted perfectly.”

Heinlein later explained. He was working up a story background around Economics in One Lesson, and that one word, TANSTAAFL, functioned perfectly as a motto for that society. At the time he made a note of it on one of the three-by-five index cards he carried everywhere with him, for just such flashes of inspiration, and it entered the mix that had been accumulating for some time. Virginia Heinlein later recalled:

“I suppose that all of this society in The Moon is a Harsh Mistress arose out of discussions that Robert and I had. What happened was that we held a number of discussions (and I remember them well) about ideal government. The problem with government is that, given some areas to make laws about, they move out into other areas, until all freedoms are gone.”

Robert A. Heinlein: In Dialogue with His Century, Volume 2: The Man Who Learned Better (1948-1988) by William H. Patterson Jr.