As a Buddhist I would consider that “innate natural reaction” (and I agree that it is) to be an emotional neurotic issue. The person who takes the bigger piece of the orange also has neurotic issues or he’s psychotic and has no emotions about it at all.
As for the action being unfair that is a mental fabrication overlaid on the reality of it. The reality is that one person took more than half and that’s just how it is. There might be a number of reasons for why he did. Selfishness, lack of mindfulness, stupidity, poor vision, ... without a deeper knowledge of the reasons for his actions one can’t determine intent or lack of intent so even by the artificial concept of fairness it’s not possible to know if the rules of fairness were violated.
FWIW I think an understanding of what fairness really is and is not is relevant and on topic. You also began this as a discussion intended to lighten things up so this take on it is on topic in that respect as well.
But this is your thread so you are the final arbiter of that. It’s only fair. :-)
I love it!!! I might try to ruminate a bit on your thoughts before responding, but the reply is much appreciated.
But it might equally well be the other way round. It could be that life IS fundamentally fair, but that by Human action (or inaction) we have collectively made it unfair. You may slur the "innate natural reaction" an emotional neurotic issue, but the fact is that it IS innate, and innate in all Humans, (unless, as you say, they are psychotic).