I think it's more that a successful meme is one that can convey an idea on its own, with little to no outside context needed.

Take that image of Fry squinting his eyes while not sure if X or Y. One doesn't need to have seen Futurama to understand any given variant of it. Same with the one with bender making his own X but with blackjack and hookers. Again, one doesn't have to have seen the original episode to understand the idea being conveyed.