The social mechanism by which human beings cause other human beings to behave in a fair manner is their willingness to do things that go against their immediate self-interest just to punish those who offer unfair choices.
People who are unwilling to make such choices are antisocial.
The best illustration of this trait is the test where one person divides up a pile of money and the other person either takes the deal, splitting the money as the other person chooses, or refuses the deal so that neither person gets the money.
Be the person who only accepts the 50/50 split.