This is conflating the selection and treatment effects. The difference in earnings between people who would be admitted to a Master’s programme if they applied and those who actually apply and graduate is going to be far smaller than the difference between a random Bachelor’s holder and a random Master’s holder.
I got the "everyday millionaire" book, by Chris Hogan (part of the Dave Ramsey 'gang')(haven't started reading it yet). From comments I've read in Reddit about that book, it seems like the vast majority of millionaires mentioned are lawyers/doctors, and you can't become neither without going to Uni.
They guy I was referring to in my post above, started with a certain wealth (even if that wealth is in a form of a 200-sheep-herd), a certain skillset (assisting his father in the business while growing up, having a 'knowledge base' right there in his home, having connections, having the equipment). What has gotten him to a few thousand animals since, is hard work and "invest in knowledge as you go". He didn't start from scratch.
The benefit with his line of business, is that the wealth/skills-handover was happening since he was 10 (experience, skills, knowledge). If one is to become a doctor, the mental training may start early on, but the actual knowledge is coming much later, and at a greater cost ($)(especially in the USA).
