<P> 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 popularized the phrase by using 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 '' . </P>
what does the phrase theres no such thing as free lunch mean in economic terms
opportunity cost