The Harvard economist John Kenneth Galbraith had a famous quote in a book he authored back in 1990: There are two factors contributing to euphoria (bubbles): The first is the extreme brevity of financial memory, and the second is the specious association of money and intelligence.
Ten years is a life time in financial market.
You have Fed QE, CD interest rate of 0.1%, mortgage rate of 3% (8% prior to crash), practically free money after tax and inflation. So, a few early birds, who could, borrowed. The herd then followed. And the cycle started all over again.
You .
Now you understand why many of the recent ET posts are predicting a crash.