<P> "There ain't no such thing as a free lunch" (alternatively, "There is no such thing as a free lunch" or other variants) is a popular adage communicating the idea that it is impossible to get something for nothing . The acronyms TANSTAAFL, TINSTAAFL, and TNSTAAFL are also used . Uses of the phrase dating back to the 1930s and 1940s have been found, but the phrase's first appearance is unknown . The "free lunch" in the saying refers to the nineteenth - century practice in American bars of offering a "free lunch" in order to entice drinking customers . </P> <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 do economists mean by the acronym tanstaafl