The subsequent paragraphs address that, I think. It does not have to be this way, but the reality is that most people spend as much as they earn. You know, anecdotally, I talked to people in the Bay Area who claim that they couldn't really save any money even if they wanted to, because they were only making $120k a year. But I don't think it's a US-only phenomenon; it certainly happens in Europe, too.

I suspect it comes down to a belief that a raise entitles you to a better life, right now: so you go out and buy more expensive groceries, get a nicer car, etc. I was actually raised in a fairly poor family and it's a habit I picked up very early on; took me a fair amount of work to overcome this.