@grimalkina little story time.
When I was young, I thought meritocracy was real.
I was from a (very, very) poor family from a tiny village in the middle of French Alps, away from civilization (my dad, who was born in the village itself, didn't even had running water as a young child and electricity came when he was young adult). Still, I was among the best suited for school, and later successfully passed selective exams to French Grandes Ecoles.
What an amazing proof of meritocracy it was.
But of course it's not.
For one thing, I just love studying, and i loved school since teenage years, so the merit of doing what you like is meh, at best.
And also, as a young adult, I read a paper about how socio-demographic class are often preserved from grand parents to grand children even if parents have a vastly different class, especially when grand parents where of an upper class.
I didn't find the paper back, but it was rather simple: even if the parent was poor, he benefited during his childhood from the social security and well being that upper class parents bring : better education, better health care, better relationships, etc.
This security pass to their children. It's amplified if the grand children / grandparents keep relationships.
That was exactly my case. My grandfather went to the best French Grande Ecole in 1942. He was then director of several chemical factories and when I met him as my grandfather, he was still learning computers for fun, and most of my cousins where from upper class. My mother, the youngest of 6, prefered to move far away for the love of mountains and my kind father as a young adult, even if it means an hard and simple life.
So, surprise surprise, I was absolutely not the best fruit of meritocracy, just a child from an upper class family who happened to have poor parents, but still took the most of the security and privilèges of that environment.
And moreover, my parents where extremely sane and loving and caring. Really, that was unfair advantage, and I still thought it was my doing for a couple decade or so.
The paper is right: it's so easy to believe it's your doing. Externalities are always harder to account for, especially if they are not in your favor.