[acronym, from Robert Heinlein's classic SF novel The Moon is a Harsh Mistress.] “There Ain't No Such Thing As A Free Lunch”, often invoked when someone is balking at the prospect of using an unpleasantly heavyweight technique, or at the poor quality of some piece of software, or at the signal-to-noise ratio of unmoderated Usenet newsgroups. “What? Don't tell me I have to implement a database back end to get my address book program to work!” “Well, TANSTAAFL you know.” This phrase owes some of its popularity to the high concentration of science-fiction fans and political libertarians in hackerdom (see Appendix B for discussion).

Outside hacker circles the variant TINSTAAFL (“There is No Such Thing...”) is apparently more common, and can be traced back to 1952 in the writings of ethicist Alvin Hansen. TANSTAAFL may well have arisen from it by mutation.