Was the US stock market boom predictable? | Robert Shiller

Major shifts in the economy should be foreseeable, but no one forecast such massive rises

Should we have known in March 2009 that the US S&P 500 stock index would quadruple in value in the next 10 years, or that Japan's Nikkei 225 would triple, followed closely by Hong Kong's Hang Seng index? The conventional wisdom is that it is never possible to "time the market". But moves as big as these, it might seem, must have been at least partly foreseeable.

The problem is that no one can prove why a boom happened, even after the fact, let alone show how it could have been predicted. The US boom since 2009 is a case in point.