Let's say that I'm getting by, but only just. There's things I'd like to do - take a vacation, or replace the carpet, or trade up to a better car - but I don't bother thinking much about them, because there's no point. Those things I can't do bother me a bit, but I don't dwell on them very much.
Now my circumstances improve. Now I can take that vacation, or replace the carpet, or trade up to a better car. But note that I said "or", not "and". I can do one of the things I want, but only one. Now each of those things is realistically possible, and I can seriously consider doing it. But in the end, I can only do one of them.
In this way, it's possible to have more money, and therefore more options, and still feel worse about the things you can't do because you don't have enough money.
Not even self-employed, which is great but goes opposite to stability, and some goals I have in life are not financial.
This isn't valid for 100% of the folks obviously, but say 90% fall into this trap one way or the other. It is paradoxically easiest for folks already burdened with ie mortgage, because usually the motivation to pay it back sooner trumps the need for some extra gadgets and to show off.
You know what's funny? Their overall long term happiness and life satisfaction doesn't improve a bit. In fact, in many cases it goes down due to ie extra worries about good investments, plus you earn cash by doing extra work.
Myself I increased my net income compared to my first full time IT job more than 20x in last 15 years, and I can tell you happiness comes from different place. Money just help a tiny bit on the path to it, that's all. Some folks, especially those competitive that article talks about, will never be truly happy. Of course is you live in like US with utterly broken healthcare, in some cases money can actually mean saved/improved life, but that's a bit special use case.