1. There ain't no such thing as a free lunch; something advertised as being "free" will invariably have hidden costs.

Usage notes

Quotations

• 1966, Robert Heinlein, The Moon Is A Harsh Mistress,

  "Gospodin," he said presently, "you used an odd word earlier--odd to me, I mean..."

  "Oh, 'tanstaafl.' Means 'There ain't no such thing as a free lunch.' And isn't," I added, pointing to a FREE LUNCH sign across room, "or these drinks would cost half as much. Was reminding her that anything free costs twice as much in long run or turns out worthless."

• 1985, Lance Parkin, The Infinity Doctors, page 229,

  'Tanstaafl. There ain't no such thing as a free lunch. We both know that I was brought here for a reason. If we could get down to business.'