The Broken Ladder is a sociology book that is concise and to the point. I highly recommend it. Keith Payne's thesis is that most of the negative issues we associate with poverty or income are statistically proven to be more correlated with inequality and status. And this is not a human thing, as animal studies show that this is a deeply rooted behavior of social animals like monkeys and has a genetic component that can be demonstrated to as simple creatures as fruit flies.
There are nine chapters in the book, each focusing on a particular characteristic of effect of social inequality. We learn that just having available a sum of money or a set of resources is meaningless to the individual. Instead, more important is how different those resources are from other people in the same group. Inequality leads to stress, which in turn leads to toxic behaviors, health problems, developmental issues. It leads to risk taking, to polarization in politics, it affects lifespan, it promotes conspiracy theories, religious extremism and racism.
It is a short enough book that there is no reason for me to summarize it here. I believe it's a very important work to examine, as it touches on many problems that are present, even timeless. Written in 2017, it feels like a explanatory pamphlet to what gets all the media attention in 2020.