Happy by Roko Belic and co.
People respond really well to really bad events.
The nervous system is an integrator—it integrates differences, all it can tell are differences.
People who get in flow more are happier.
And more about the historic-sociological insights I was after—after basic needs are met, about where one can shelter and when one can eat, a person’s natural happiness can be expressed. So slums—that’s sufficient stability(?) to provide happiness to flourish.