it is ONLY common in industrialized societies. in agrarian societies, everyone is a farmer, and thats all anyone knows. it takes one year to learn how to farm, and your education is complete.when you get to the point where a society needs 200 different types of work done to survive, no one person can do every specialized job, or each person would need 200 years of education to each each job. so we break it up, and everyone lears one job very well, and lets other people do the other jobs that he needs done occasionally. it makes work much more efficient.
This allows common folks to learn more and more about less and less until they know practically everything about nothing.
At the top of the pyramid, it allows leaders to learn less and less about more and more until they know practically nothing about everything.
And then there are wise guys like me that actually DO know everything!