[coldtea]

>There are plenty of counter examples of other people who are born in the same month than me who are totally different.

That's irrelevant though. He didn't say it is a law of nature that forces development in the same exact way. Just that it's a factor.

What is the concern is how a statistically significant part of those born at X months are affected, compared to those being born at Y months.

Not whether there are exceptions. Of course there will be. People being the same in both groups might even be the majority. But one group (say "born in spring-summer ) having 17% more of something compared to the other is a big thing, and that's whats considered here - even if the rest 83% are the same on that aspect.