It's simple maths. Wherever you live, there's a baseline amount of money that it costs to survive. Food costs the same whether you're rich or poor. Housing varies, but there is generally a baseline. If the baseline cost of living is $2000/month, and you make $2000 a month, you have $0 disposable income. If you make $4000 a month, you have $2000 in disposable income. If you make $8000 a month, you have $6000 per month disposable income, or 3 times that of the second scenario. Since the cost of certain things is constant, as you make more money, your disposable income rises dramatically (until a certain point where gains are seemingly only incremental, at which point you're no longer middle class).

The rich have more opportunity to save, thus they learn about saving. They have capital, thus learn how to use it. If you never save and never accrue capital, you'll never understand it. So any time you do end up with a windfall, you will inevitably squander it, since you've never had the experience of what to do with it.

Plus, money problems lead to stress. My wife grew up poor, and even though we're not doing badly today, it causes an immense amount of stress and is 'mental overhead' for her. She never wants to invest, is apprehensive about going to school herself, or basically doing anything that would deplete any amount of savings. This inevitably prevents her from attaining a 'higher' equilibrium, but I do understand the feeling (and for the record, based on where she came from, she's actually doing fantastic and has experience doing things that none of her relatives even contemplate doing). I grew up working class for this country (so probably the bottom end of 'middle class'), but I'm stubborn with a bit of a gambling streak. So I'm going to university, investing money, occasionally hustling for extra here and there (gambling, side jobs, etc...), and it's mostly going OK.

Plenty of relationships end over money. And when your world is falling all around you, it's all too easy to turn to 'escapes' such as drugs and alcohol.

This is a tech forum, so a little analogy. A poor person is like a phone whose specs are just barely enough to run Android. The experience is poor, laggy, and you can't play too many games, or do any 'productive' tasks. Middle class is like an iPad pro or a decent laptop, you can do what you want for the most part, it's a pleasant experience, but there are certain limitations. Being rich is like having a super-computer - the potential is seemingly limitless, you can solve problems that are out of reach of the first two.

Right now I'm in University, and being working-class, it's hard to compete with rich kids who live on their parents dollar. Every day I work is less time to study. Every time I have to cook dinner is less time to study. And if I need to study a 'minimum' amount to pass my courses, then I need to either sacrifice sleep or time with my wife. And neither leads to a particularly great outcome. So mostly I just suck it up and lose sleep, live off coffee, and am a solid 'B' student rather than actually competing with the more privileged kids. In the job market I'll probably have to use my life experience and hustling streak, since I won't compete on GPA or extra-curriculars.

Anyhow, just a few thoughts on the matter. And these sorts of problems with income inequality are why more and more economists support the idea of a basic income. It'll allow the 'poor' to have the ability to have disposable income with which they can get an education, or invest in themselves rather than work like dogs to barely survive. While this may not seem fair for those who have already attained middle class or higher (who always claim they 'earned' it, never mind the societal advantages they used), it's better for society. Unless you think having a serf class is a societal advantage (and there are people who think this)...