RSL wrote:mrj - Google "Kondratiev wave"
I had this explained to me by Dennis Wobeser (he always made me think) and human nature and long cycles are a good reason why grandparents/tribal elders are best equipped to teach youth as they will experience similar parts of the cycle through their life at roughly the same life stage. It is interesting stuff.
There is a man I dearly miss. He passed the same day as my brain surgery in 2015.