I don't take his advice as a literal exact prescription. I just take it as: carefully consider how you earn your money, and how you spend it, oh and by the way here are some examples.
I'm not really interested in retiring early. Many people seem to have the idea that they should work hard for 40hr a week for 40 years so they can then work 0hr a week for 20 years. Some of the FIRE crowd adapt that by saying, "well if you're frugal, then the 40yr work becomes 20." But it's the same thing, really.
But there are other options. For example, if you're frugal then you're essentially living on (for example) 20 of your 40 hours a week - so why not just work 20hr pw forever? Or, let's say you want to live on $40k, rather than doing a job you hate for $80k and then bailing on it after 20 years, do a job you love for $40k. Or maybe you don't give a damn what you do for a paid job, but you really care about your children, or volunteering for the Red Cross - so you do a job which you may love or hate, but you aren't that bothered by it, because it funds this other thing you do love to do.
And so on. There are many possibilities. The point is not that this or that lifestyle is ideal for everyone, but that the life you choose should be one you choose after careful thought, not one you just drift into. Many people just drift into things and then are unhappy.