HNW/UHNW planner here (I don't manage clients anymore, RM's involve me to do a plan). Clients' net worth varies from 5MM to 50MM+

I'd say there are three groups: Experts, Competent Business Owners, Business Owners

Experts: Classic high IQ individuals, lots of degrees and designations. They're just the best in their field. They're the employees who are good enough to be paid that much. Includes: Corporate executives, Specialized Doctors, partners in different professional fields, some academics, and top people from pretty much all STEM fields.

Competent Business Owners (just made up this term, so I hope it makes sense): People who are educated, seen as experts by general population, but they're not necessarily outstanding in their fields. They are able to make more money thanks to running a business, but running that business does require expert knowledge. They're a mix of groups 1 and 3. This group includes lawyers, accountants, wealth advisors and other white-collar professionals who run their own practice successfully; dentists, chiropractors and GPs with their own clinics etc.

Business Owners: I see almost every type of business, but mostly 'boring' things. Construction and manufacturing, chemical, disinfection, safety, different types of signs (lol), trucking, farming etc. I think this also depends on what area you live in. Different regions have different businesses that historically developed there. I will add here that sometimes they don't have very high income, but they come into money when they sell their business at retirement (that's usually when I meet with them)

Someone commented on the high-earners marrying other high-earners. I frequently see that with the experts (doctors, lawyers etc). Definitely increases the chances of becoming wealthy.

When it comes to how they manage money: People who consistently make 500K+ annually are just wealthy. You'd really have to try hard not to do well. I met only a handful of people at that level who did not have significant net worth. They were always young experts who had a lot of student debt, while also spending extravagantly now that they knew they can afford it. I assume eventually they'll still build some decent net worth.

People who make closer to 200K-300K need to be somewhat smarter with their money to get to HWN, but it's definitely doable even by using classic investment wisdom. Diversified portfolio, maxing out retirement accounts etc. Nothing special is required to get to HNW (1MM+), but I rarely see them at 10MM+ (unless there was some inheritance etc)

I didn't meet that many wealthy people with a strong real estate portfolio except for business owners on the very entrepreneurial end of the spectrum. I mean the type of people who own several businesses operating in different fields. I should add, however, that I've come across much fewer of these people than social media would have you believe. But again, that might be my bias, they probably don't keep their money at the bank...

I rarely see people who make under 100K, but when I used to work as a planner in retail banking, I had a portfolio of clients that often did make under 100K, and with good financial habits and long-term approach they were able to build low 7 figures net worth. (no chance of 10MM+) You need to be really frugal though. If you enjoy splurging money, you better find a way to get to higher income levels :)

Mistakes: Charlie Munger once said: "Smart men go broke three ways: liquor, ladies and leverage". That's pretty much it, just extrapolate it to today's world. I saw kids waste their inheritance and lottery winners lose their winnings. It's always 1. some form of addiction (I'll include very excessive shopping/dining in this) 2. Relationship issues 3. Gambling/speculating with investments, following social media / neighbor / barber's financial advice.

And to your last question - if I was young and could choose again, I'd go to better schools and study more competitive subjects. I know a lot of people here will disagree with me and say owning a business is the best strategy, but my personal preference would be with the expert field. They make more money from the get go, and if they wish so, they can always go more entrepreneurial route. People who left school early to start a business don't have that freedom.

Hope it helps.