Everything is about survival. Everyone wants to be on top, everything wants the most money, everything wants to look the best, everything wants the most power.
Why because if you had all that it's pretty damn hard to be depressed and for your survival to be jeopardized. There is nothing wrong with wanting to be at the top because it increases your survival % which makes you happier, healthier, and more peaceful.
But the reason man made concepts like justice, fairness , honesty, etc are implemented is because realistically humans cant operate without them. If we tried to operate without them then literally everyone would be killing, stealing, etc against eachother to reach the top and only the strongest and smartest would eventually win. But at the same time that would create so much chaos that eventually everything would just be destroyed. So whether or not there is justice in the universe without the concept of atleast trying to live like there is and implementing justice/fairness to some extent then humans would die off so damm quick trying to reach the top. So people have to treat each other fairly whether fairness is manmade or not since it's unrealistic for any long term progression of humanity if everyone was unfair to eachother.