Deborski -- напрасно and the synonym зря -- both mean "in vain; for naught" -- are heard in the classic Soviet-era pop song Разговор со счастьем. I would definitely call it a "must know" song because it's so famous and contains some useful vocabulary and grammar. Here's a version with karaoke lyrics:
Yeah, Throbert, I totally misread the word in the saying and translated as "написано" - written. It makes much better sense now. Thanks!