The approach I take with quotes is more subjective than it is with almost all of my other cards, since it would pointless to really judge whether or not I know some piece of maybe abstruse wisdom, I just rate it on a subjective grading of, how well am I living my life relative to this statement, and if it feels like it's something I'm really lacking I'll fail it or mark it hard. The card has no back, something that I also do for more axiomatic pieces of CS theory as well, where it's too difficult to meaningfully capture the whole idea in many different question-answers.