Its mostly luck. At least in a majority of cases.
Luck determines your genetic traits, your starting lot in life, and it determines what your development is going to look like. It also largely determines how easy it will be to make it through college, how you will build initial equity, and what sort of networking/investment opportunities will be initially available. That accounts for a staggering amount of your later success.
From there it is a lot of coasting where smart, hard work can be a difference maker, but often companies/people aren't rewarding hard work so much as they are rewarding interpersonal relationships and meeting a baseline for acceptability, which often includes traits and characteristics that have little to do with how hard you were working. Most people, in my experience, actually see grinders as tools to utilize, not so much promote. You want a grinder and excellent worker to make your life easier, not get boosted up to your level. This was the case in my experience working in bars/restaraunts in college, up to corporate America at varying types of companies, big and small.
In terms of entrepreneurship, again, a lot is in who you know. I personally had the opportunity in one of my jobs during and after college to be around a lot of CEO's and incredibly wealthy people. Each one you could find a very rosy bootstrap narrative of how they went from rags to riches, but it was mostly bullshit. All of them, every one, either had wealthy parents that allowed them to take risks most could not, with the fallback to fail multiple times, angel investors that involved family and friends that walked them along the way, or the right connections because of fiends/family.
