Even if you’re right that the very concept of fairness is a Human construct, its still one that, by definition, Humans value and indulge in.
Absolutely true! But not everyone plays the game and you have to deal with that. How you deal with it is a reflection of mental, emotional and spiritual maturity and others will overlay their concepts of fair judgment on that. Fairly or not.
You have to evaluate your own reactions to “unfair” circumstances by what you want out of yourself. Is “winning” the situation going to serve you best or are there other standards you want to apply to yourself?