"Not one person in your life's journey is met in vain"?
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:



"Всё на свете было не зря
Не напрасно было!"

PS. The song originally appeared in a 1973 comedy where it was performed by a bunch of dancing maidens in the court of Ivan the Terrible -- so the folk costumes and the crazy wig-spinning at the end of the video are a parody of the scene.