Understand that there are two worldviews out there with regards to healthy finances. There are those that have a problem with debt, they recognize the risk you take on by obliging yourself to a negative cashflow situation. We have a risk aversion to this situation, even when it would make good financial sense to take on debt, many MMM still avoid it with pathological obsession (myself included).
But then there are those that do not have a problem with debt. Their risk tolerance for the negative cashflow situation is very high.
We can pass all the value judgment aspersions on this second group we want, but if you want to know how they "afford" these things, you just need to realize that to the extent you are OK with debt, then as long as you can afford to pay all of your monthly obligations, you actually are doing fine.
To clarify, it isn't a choice I would make, and I don't see it work out well long term for anybody, but that's what they think about the situation.
So if the median wage was 40k, and lots of people have a spouse that works, then you're looking at 80k as a reasonable estimate for household income in many of the places we MMM folks are going to be living. Probably 80-150k more likely (this isn't a poor man's internet hangout spot).
So if you're making close to 5k/mo after taxes, you can "afford" a shitload of stuff. You and I wouldn't make this choice, because being one paycheck away from oblivion isn't fun for us. But some people can tolerate that feeling better (maybe because they just aren't aware of it).
Then you really dig into it, and tear into people's finances. That 40 something that has always lived in their own house and owned their own new car? Well, they've usually held down a job too, and they've earned close to $1 mil just off wages. Even spending like a knob you'd be hard pressed to have nothing by then. The forced savings account of a mortgage and a car note have probably made it so they have a net worth excluding debt of around 200k by the time they're 45. So you look at their total debt number and it looks insane to you, but their debt to equity ratio might be better than the 20 something mustachian who is OK with a high mortgage number.
What I think a lot of people don't see is the total history of the folks you interact with. If one of us hit age 40 and decided that we'd had enough of FIRE, re-entered the grind making as much as we could, and lived off that new amount, in some hedonistic post FIRE splurge, we'd be in a situation where we could FIRE at any time and yet can still live an insane lifestyle.
And you can read through the postings to see people that do exactly that.
But I don't think that's the way most do it. I think most end up with a high long term debt payment in their 20's (mortgage or student loans or both) such that they get used to the idea of a debt payment, and then they just keep tacking on more and more.
As one of those types described to me "to the extent you have debt, it doesn't really matter how much." He was trying to explain why it was OK for the government to to keep borrowing money in a limitless way, but that he could even utter that sentiment made me feel all hollow inside.
I recently met up with him after spending several hours (after he and his wife specifically asked) walking through how to improve their financial situation. We went through each debt, each payment, talked at length about what their action plan would be, them nodding the whole time, about 6 months ago.
They drove up in a brand new BMW 6 months later. *facepalm*
But it works for them. They've been living this way for a decade now. IF it all falls apart at some point, then maybe it wasn't a good idea, but it may very well work out fine, and it is their choice to make either way.