You seem to be blindly lucky and do not really appreciate that...
It can take more than intelligence and luck, it could take a desire and a choice to make money a big priority in your life, which it rarely was for me.
If Bill Gates had said "Fuck Microsoft, I don't want to do this shit anymore" and quit early on in his career, (which, if he had free will, he could have done at any point) then he probably wouldn't have wound up the richest person in the world, no matter how lucky he was.
He chose to do what he did (didn't he?), and that (in large part) was what made him unimaginably rich.
Its clear that you need to be lucky to become a billionaire but i think a more interesting question is how much luck is involved in becoming a multi millionaire.
Parenthetically, I was born poor. My family had very little money when I was born, and what little they had they left behind in the old country when we immigrated to America. So I was poor when I was really young, and middle class by the time I left high school, thanks to the hard work (and maybe luck) of my parents.
But your point is taken... if I was really poor when it came time to work and I refused to do so, then I'd feel the lash of the economic whip, as I'm just about to do so now as I've burnt through my savings yet again....
So, while I think that personal responsibility is a valuable perspective, I do think that ultimately what you describe boils down to "luck".
"The team shows this by ranking individuals according to the number of lucky and unlucky events they experience throughout their 40-year careers. "It is evident that the most successful individuals are also the luckiest ones," they say. "And the less successful individuals are also the unluckiest ones."
This article kind of assumes everyone wants to be rich, or makes that a primary goal in their life. That's not really the case.
Some people are more career-driven, more ambitious, more interested in making money. Others have various psychological issues that prevent them from working effectively or sometimes getting or keeping a job at all. Is that just bad luck?
I grew up despising money and looking down on people who chased after money. I didn't want to be that guy. I did reluctantly get work, but I never tried to climb the corporate ladder, refused offers of promotion to management, took many years off work and lived off my savings instead, and I've burnt out many times, my career suffered as a result. Is that just bad luck?
I had a chance to work at Google early on, pre-IPO, but I decided not to. I worked at a small financial company for a year, was offered a big promotion and turned it down and quit instead, because I was burnt out and just not interested in that job. That company wound up becoming one of the largest financial companies in the world.
Being depressed much of my life, I didn't really care to plan for or save for my long term future, because I thought I wouldn't have one. This has become a self-fulfiling prophecy in some sense, though not how I expected. I didn't think I'd live, but I did live, just not with as much financial security had I pursued money money more and saved for the long-term.
In many ways I've been lucky. I grew up mostly in safe suburbs when I was young. I went to some great schools, some of the best in the country, but also dropped out of those. I'm not ambitious. I get bored easily. I like to follow my own interests rather do boring work other people tell me to do. I suffer from depression and just generally don't feel I fit well in this world, but also consider that I'm not rich (actually close to becoming homeless at this point) due in large measure to my own choices rather than pure luck.
Now, you could argue that we really have no free will. If that's so, then yes, where you are could be said to be "just chance". But to the degree we could make good or bad choices, we bear some responsibility for where we end up, though clearly luck plays some role, and it's good to be in the right place at the right time, doing the right thing.