Source

The Bubble needs fresh bullish investors:
Above all you need to have people that were not apart of the previous bubble.

Quote:
“Let me describe the nature of a [stock market] bubble: First a real bubble needs above all to get rid of the old fogies. So you can’t have a bubble five years after a bust. A bubble needs to rotate serious investment professionals out of their jobs…

The pattern appears to follow a generational cycle. Sure, the statistics are a little flimsy, but if you think about it, the generational idea does make sense: After a market crash, it takes a generation to clean out the skeptics and usher in a new class of bullish investors.”

The 17 year cycle
Quote: “These cycles tend to last around seventeen years. For example, the 1980s and the 1990s were paper years. The late 60s and 70s were hard asset years. The post-war years from mid-1940s to mid-1960s were paper years.”