The overarching point of the author is that most of his target audience (and those reading HN) are used to being thrifty and not spend money at all, even when they get older. They fail to realize that at some point, it's worth your time to spend the X amount either because the value of investing X down the line is so great, or because the time saved by spending X is now so much greater than before, because of something changing in your life (career has progressed, valuation of free time has changed).
I definitely see this myself daily, ending up wasting few minutes each day on trivial things that add up, while it could be fixed by paying a small amount.
Or for example trying to wade through a free course to learn something, but ultimately just dropping it out of no motivation. Compared to paying for a course, which makes you more responsible s you paid for it and usually also offers more effective training.