I think the root cause of all problems is cognitive dissonance.

   You predict something will be a certain way, based on what you
   know from the past.

   You observe/experience something happening that's different than
   your expectation.

   You compare the two. This all happens quickly. Remember: We
   don't see what's happening NOW - we see what JUST HAPPENED a
   moment ago.

   When they don't match up, then "THAT'S NOT FAIR".

   I think it's also the source of all learning too. We resolve
   cognitive dissonance by finding something within our minds to
   analogize to that we DO understand, and graft the new concepts
   on. Also, by the time kids can talk, they've learned most of
   what they need to know in life. They've absorbed our culture,
   within which Plato is pervasive.. in all of our religions...
   East and West... all of our ideologies... remember, HE came up
   with the very CONCEPT of idea.

   Fairness is a cultural thing. It's taught. Learned. I don't
   think it's instinctive. But cognitive dissonance seems to be
   built-in, our reality comparator. It's the only answer I have
   for "Why does a baby cry?" Cognitive Dissonance doesn't even
   require language that we understand nor does it even require us
   to be human.