As others have mentioned, there are many paths to FIRE, and we're all perfectly within our rights to take the path we think is the best for us. MMM writes about what he knows, and that's fine. But I think one area where I disagree with MMM is his weighing expense reduction as far more important than income increase.
His blog has the specific angle of expense reduction because, as he's admitted, he started from a position of privilege: a $66k starting salary in today's dollars at age 22 for a brand-new bachelor's degree holder is unthinkable to me and virtually everyone I've ever known. Nobody told me at age 16 when I was starting college that the degree and field I choose--if not course-corrected at some point--would quite literally dictate the direction and quality of my working life for the next many decades. Also, he got a 39% raise in his first year of work and continued earning steadily more nearly every year after? I've never heard of more than a 2% routine raise...again, that kind of good fortune in one's day job is unthinkable to me.
For the reasons above and many others, I think many middle- and lower-income folks would benefit from a more balanced approach that dispenses tips for both reducing their expenses and increasing their income (while not succumbing to lifestyle inflation). I've benefitted so much from tips on other FIRE blogs for using the gig economy, continued education, real estate, and other amazing resources to try and set myself up for better earning in the present and future. I'm privileged enough to still have many ways to reduce my expenses, but plenty of people aren't in the same boat...especially if they have a large family, chronic health issues, or are socioeconomically disadvantaged.