Why is it fair that some people are rich and others are poor?

It’s fair because we learned to accept it through storytelling.

Various social animals show signs of reacting negatively towards each other when they are losing resources or attention. Whether this behavior qualifies as ‘jealousy’ in the human sense is debatable, but their observable actions suggest something akin to it.

Go back in time to the first humans. They would have been displaying that same type of jealous behavior seen in animals if one member of the group was hoarding most of the food or taking a mate’s attention away from them. At some point in early human history a division of labor was established among a group and the outcomes of the different labor were not equal. That would have led to infighting and possible murder that would have harmed the whole group. But a miracle of human thought happened, a story was created that allowed humans to set aside their jealousy when faced with inequality.

Do you reward the big strong alpha hunter with the largest portion of meat because he did most of the work? You’re going to tell the group stories to support why that’s fair.

Do you give the children the largest portion of meat because if the weakest among us aren’t strong then the group as a whole is not strong? You’re going to tell the stories to support why that’s fair.

That ancient story established a viewpoint that informed myths. That informed philosophy. That informed economic theories. Whatever that story was, it is the greatest story ever told! I may be channeling my inner Joseph Campbell to suggest it was a single story that sparked a revolution of thought. More likely many competing stories emerged before one leading narrative took hold.

The moral implication of “fair” in your question is subjective to what the dominant culture defines as fair. Many commentators reply that the rich work hard so they earned it. But that is not a timeless truth. In the first hundred years of American history, both slaves and freemen worked hard, but only one group profited. During the Gilded Age hard working industrialists got very rich and then the government increased taxes because it was determined they got too rich. In both cases, storytelling was used to justify these events to the masses, framing them as ‘fair’ in the context of what best served societal survival at the time.