@a83 I don't really understand this question. To the extent that I do understand it, the answer is obviously not.
I don't know what you think being upper class is, but let's just say that it's having wealth in excess of $6M. That puts you in the 1%.
Source.
I don't know exactly what you mean by being an entrepreneur, but let's say that means starting a new business.
Putting those two definitions together, you're asking if the only way someone could have more than $6M is by starting a new business. The answer is obviously not.
Take your hypothetical heart surgeon, earning 800k annually. That person has a takehome pay of around 40k per month. If they invest 20k per month, getting 7% real returns, they have the $6M in less than 15 years, and they haven't started any new business.
There are many other ways that people enter the 1%: inheritance, buying into an established, profitable privately held company, royalties, and even selling their labor. Famous athletes, actors, and singers sell their labor. But CEOs also sell their labor for millions of dollars.
It's true that you're unlikely to become a 1% person by waiting on a long-lost relative to give an inheritance, and few people are famous celebrities or even brilliant surgeons or CEOs. But, most entrepreneurs aren't in the 1% either. Most run small businesses that squeak by for a few years until they become insolvent. The truth is, it's hard to be in the 1% because there are lots of other people in the world.
Personally, I don't really care about what bracket I'm in. I care about having enough money to meet all of my needs and some of my wants, and getting the chance to do work that I find meaningful. I'll let someone else worry about my level of wealth and income.