It just has to be this in the story because it doesn't want to engage with why what the earring indicates is so good except that it provides unfailable "happiness". It implies a static world where "the right decision" always exists, but doesn't want to engage with the details. It also implies a kind of akrasia[1] that I don't think resonates with lived experience: "happiness" is a state we pass in and out of, not the accumulation of correct decisions. We undergo unhappiness for the sake of future happiness. "Happiness" is a questionable end-all goal first of all, but either way not even the kind of thing ontologically compatible with the author's framing.
It just feels half-baked, it doesn't actually say anything even when it has all the pretenses of that. Maybe that's too harsh though.
Maybe I am just not smart enough for this.. What is the parable supposed to be about? What are we supposed to learn from it?