I assumed he meant that two twins growing up under completely different circumstances will still turn out to be the same. Which then implies to me that success is already determined before birth. If true, working our young people hard or not working them won't have any profound affect on their lives.

Incidentally, my upbringing sounds a lot like kstenerud's. My brother and myself sound much like he and his siblings. Another anecdote, sure, but still an intriguing point of view.

the problem isn't the conclusion he drew, it's that he made a causal link (at least he used causal language, "as a result we grew up X") instead of drawing a correlation. This would be wrong regardless of whether the conclusion was actually correct because no matter the conclusion, his experience is insufficient to make that causal link with high confidence.