we all go too school on the same calendar cycle. But to young children one year difference can be quite significant.
this magnitude of difference diminishes with age: 50 vs 51 years old? same thing... 3 vs 4 years old? may be the difference between pooping your pants and holding it in
but consider the social consequences of shitting your pants in a semi-public setting? and add these up over your whole k12 education across millions of people.
the idea is that some psychological traits will be formed by this. and the zodiac reveals when you where born.
in summary I'm saying that taking all these things together and averaging them out may reveal psychological traits formed by an homogenized (standardized) education experience.