月は無慈悲な夜の女王
The phrase and the acronym are central to Robert Heinlein's 1966 science-fiction novel "The Moon Is a Harsh Mistress", which helped popularize it. The free-market economist Milton Friedman also increased its exposure and use by paraphrasing it as the title of a 1975 book, and it is used in economics literature to describe opportunity cost. Campbell McConnell writes that the idea is "at the core of economics".