I have a group of friends who I have known since I was a kid. This is useful in that, while it’s of course anecdotal, I can say that it’s a sample of people who all knew each other before any of us were capable of earning money.
Within this group, there is zero correlation between intelligence or work ethic and wealth/income. My wealthiest friend inherited his family business. My second wealthiest friend married into money. These two are among the least hard working and intelligent friends I have. Meanwhile the smartest friend I have - the one who almost aced his SAT - is doing ok but not like he’s swimming in money (community college professor - which honestly is a pretty great gig, he was smart enough to recognize that). Another truly brilliant friend of mine is doing research in a field he is passionate about but he’s definitely not the highest earner in our group.
Admittedly none of us are extremely hard workers, but I know tons of workers - especially some undocumented folks, who work way harder than I can even imagine, and they are of course making very little.