People don't want to face cold hard truths. IQ is not perfect by any means, but one of the best predictors of overall success in life. Yet when it's overlapped with socioeconomic standing, it suddenly becomes a racist measurement.
>People don't want to face cold hard truths.
Yeah, no shit. People are too busy trying to survive instead of trying to figure out life's "truths".
I think your statement is unlikely to be true. It will, of course, depend on your specific definitions, but from twin studies we've found that intelligence seems to be heritable.[0] It's even a fairly strong effect:
>The heritability of intelligence increases from about 20% in infancy to perhaps 80% in later adulthood.[0]
Other studies have found a similar effect.[1][2] Due to us observing this kind of a heritability effect (one that grows stronger as we age), I think it's unlikely that random events, such as trauma and hardships, are the main cause for lower levels of cognitive development. They certainly play a role in it, because they absolutely do affect cognitive development negatively, but I wouldn't bet money on this being the main reason.
Note that even though [2] favors the maternal womb environment over genetics as a factor in intelligence, it's still a factor that the individual in question had no control over.
[0] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4270739/
[1] https://www.ncbi.nlm.nih.gov/pubmed/24791031
[2] https://www.ncbi.nlm.nih.gov/pubmed/9242404
>Yeah, no shit. People are too busy trying to survive instead of trying to figure out life's "truths".
I think in this case the parent was referring to people who discuss and solve these kinds of problems, rather than the people actually going through them.
...define success? It sounds like you're implying wealth is a meritocracy.