TANSTAAFL is an acronym for the aage "There Ain't No Such Thing As A Free Lunch," popularized by science fiction writer Robert A. Heinlein in his 1966 novel The Moon Is a Harsh Mistress, which discusses the problems caused by not considering the eventual outcome of an unbalanced economy. This phrase and book are popular with libertarians and the phrase is often seen in economics textbooks. In order to avoid a double negative, the acronym "TINSTAAFL" is sometimes used instead, meaning "There Is No Such Thing As A Free Lunch".