The concrete part is that people with that level of income (large, but not so large as to make all problems disappear) know that to be comfortable in the future they need to save a big chunk of their income. The people living with much lower incomes just don't have that luxury at all. Which is kind of the point - it's totally different worlds.
I disagree that lost income is purely psychological. There are biological realities to deal with, especially in the US without the social safety net of other countries, that make lost income important. The first two that come to mind are the significant cost of raising children and retirement. Those are ticking clock issues to many people.
I agree they are two different worlds for low and middle income people. But we could play this game with even lower income people elsewhere in the world and reduce the issues of the developed countries poor.
I think we probably agree on the situation but disagree on what terms make sense to describe it.
For example, if you get your bachelors in 3 years instead of 4 and spend $30k on tuition and earn $90k by working, then that would result in an extra $120k in compared to spending 4 years in college.
I class it as an expense, because everything has an opportunity cost, which is defined as your 2nd best option. It is not always useful, for example thinking about spending time with your kids rather earning $15 driving for uber or something. But it could be, if you need that $15 to feed your kids.
As soon as you put "saving for retirement" as something that's even possible, you're no longer in the realm of what's genuinely "tough".
"Oh, those people making three times what I do a month have it so tough! After paying way more than the minimum on their student loans and putting aside a large chunk of money for retirement, they might only have a thousand dollars or so of truly disposable income!"
"Tough" is when "disposable income" is a fantasy, and you're regularly having to choose between whether to pay your heating bill or buy enough food for the rest of the week.
The comment I responded to was about a politician complaining about a certain payrate. To which I wanted to show that it is possible to have to have to be stretched thin (mentally), and the politician is not thinking about having to cancel their third overseas vacation. Yes, they’re not on the very last rung of the ladder, but slipping off your rung also causes worry.
6,000 EUR per month is $7,300 USD per month is tough if you’re a new pharmacist in the US and need to repay $300k of student loans and make up for 4 to 6 years of lost income and catch up retirement savings, as an example.