I think a lot of people on comfortable incomes have absolutely no idea how privileged they are.
I also know people who complain about their financial situation in the same breath that they contemplate spending £15K/year or more per child on private education, in spite of having good state schools available.
[1] https://ifs.org.uk/tools_and_resources/where_do_you_fit_in
That is before taxes and redistribution though. People without income or with _de minimis_ income would get their housing cost paid (which costs £20k-£30k per year in London, i.e. 25-40k of pre-tax salary), their council tax bill paid, their TV licence fee waived, prescription and dentistry fees waived, childcare subsidised, and would get £400 of spending money per person on top for bills, food etc.
Which is why people on zero income in London can afford to have 2-3 kids, but two people on £50k combined income cannot.
Generally speaking it all starts when you're young. The best is having poor/tight parents. The worst that can happen is you get a poorly paying job yourself and consider this normal. But there's a strong chance you'll get a better paying job and not ever have to worry about money. The worst is having middle class parents who spend their money. Now even if you get a job as well paying, which isn't guaranteed, you'll simply have what you think is normal. But there's a strong chance you'll get a worse paying job and always struggle with money.