Most of it is. Your dad can be LeBron James and you can inherit all his genes, physical characteristics, and natural abilities, but if you don't want to practice 4 hours a day, practice while the other players are playing video games, staying up late, drinking beer and eating junk food, you're not going to be successful in basketball.
Being born into a better family gives you a better chance but it doesn't guarantee you anything, just like being born into a worse family gives you a worse chance but doesn't completely eliminate the chance of success for you. 90% of it is your effort in either case.
No, it's not anywhere near 90%. That is a number you pulled out of your ass that is diametrically opposed to every finding from the study described in the article.
Hard to sustain the fiction that people deserve or earned their outcomes if hard work/effort/gumption/ambition doesn't make up the vast majority of the equation.
Establishing that most/many people are effectively doomed from birth even in the US takes a lot of the validity out of the "personal responsibility" argument.
Even so it's not that simple. If you see your parents - and all the 'mature' people in your life - doing things a certain way, then that it is the "right" way. If what they are doing is complaining how they're ont getting what's rightfully there's (vs working to make it something they earn) -- then you're going to believe that too.
In order to be able to put in the effort required, you first have to have your eyes opened to the fact that there are better ways of doing things than what you're living with every day. WOrse, you have to accept that the people you've been looking up to may be wrong about important, fundamental things.
That hurdle - that awakening to possibility - is so much bigger than any of the rest of the effort required, because people don't generally know what they don't know.
Lebron James was already playing basketball and being noticed by coaches when he was 9 years old. He was incredibly lucky to be in that position. At 9 years old 100% of you do in life is your genetics, environment and luck.
You also can't possibly believe any significant part of the difference between Lebron James and lesser basketball pros is due to effort and dedication unless you assume everybody else is lazy and partying when Lebron is practicing. He is the best (or one of the best) out of hundreds of extremely dedicated professionals.
I think that's an over-simplification. Maybe better put as: 90% of successes required putting in a great effort.
But how many equal efforts did not result in success?
I think it's fair to consider the effort (which undoubtedly is less and less important to success the more resources you start with) a minimum barrier to entry. But I don't think it automatically follows that the effort you put into something is a very good gauge of success. Or even that it's a differentiator between success and failure.
I am very skeptical of the claim that 90% of the variation between the performance of the average professional basketball player and LeBron James is effort.
Being born into a better family gives you a better chance but it doesn't guarantee you anything, just like being born into a worse family gives you a worse chance but doesn't completely eliminate the chance of success for you. 90% of it is your effort in either case.