What if that's true, on the part of the parents... Is it the children's fault? Like I said, not all parents are even interested in their kids. Some are abusive, some addicts, some just neglectful in the extreme.
That has a dramatic bearing on the child's outcomes. It's why we talk about cycles of abuse, cycles of poverty, etc. The kids often end up inheriting their parents' outlooks (and vices).
Conversely, having well-off, well-educated parents, who are invested in their child and pushing them to achieve... This also has a dramatic bearing on the child's outcomes, but in the opposite direction (positive).
I'm sure we aren't about to blame the 5 year old child if the parents decide to stick them in from of the TV or are never around to nurture or help them.
Again, all this "you are entirely the product of your own efforts" is an ideological leaning, one that is not borne out by real world data.
Do you think all children have a supportive home environment? You can't honestly believe that, surely.
You can't honestly believe either that a child's upbringing has no bearing on their life outcomes. It beggars belief if you do.