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Fairness is a fictional manmade concept. //
I don't see this.
Fairness is about mathematical expectation. Fairness means people have equal opportunity (often within a restricted domain, or ignoring certain starting conditions). There is [nearly?] always going to be a locus in which fairness is asserted outside which it is no longer the case.
* The race is fair because both runners run the same distance. Ah but the ground is uneven.
* The race is fair because the ground and distance is even. Ah but one runner is poor and hasn't eaten for days and so is weak.
* The race is fair as the runners have been nourished equally, the distance and going are controlled. Ah, but this runner's family have a genetic disposition that enables them to run faster without tiring ... et cetera.
If mankind didn't exist a situation could still be fair or unfair for a creature - a combat test for leadership is unfair because this creature had a greater opportunity for nourishment and so grew stronger than the others. That of course doesn't mean it's the wrong test, just that each creature able to take the test doesn't have equal opportunity to achieve through their own efforts.
>It's not fair to me that someone steals my car //
Everyone had opportunity to steal a car, including you, that's fair!
I don't equate fairness and just deserts [ie justice]. For example two people can compete in a fair competition but the least deserving - the one who made the least effort or the one whose lifestyle is least noble - can win; the competition was still fair though.