“Justice is nothing in itself, but a mutual pact in any place and time not to harm and not to be harmed.”Epicur · Maximele fundamentale · -280 · Maxima 33
Justice isn't written into nature; it's the pact by which people agree not to harm each other.
There is no justice written into nature, valid everywhere in the same way; it arises wherever people agree, tacitly or explicitly, not to attack each other. The mechanism is simple: if you harm no one, you have nothing to fear from retaliation, so you live at ease. That is why rules differ between communities — a property law, for instance, only matters where there is something to divide and someone to take it.
Why it matters It helps when thinking about laws and social norms: ask what kind of non-aggression pact a rule serves and for whom, instead of treating it as an eternal truth.