Former Federal Reserve Chairman Alan Greenspan said it’s impossible to know that you are in a bubble when you are in one.  It isn’t impossible for most of us, but it sure seems to be tough for the Fed. Federal Reserve Vice Chairman Donald Kohn who seems to have the same problem:

Kohn said it’s wise to beware of "false positives" when assessing potential asset bubbles, such as with rising stock or commodity prices. A Fed action to correct a bubble might include hiking interest rates, which could harm a wider financial recovery, he said.

Why is it so difficult for the Federal Reserve to see when asset prices are out of whack with fundamentals? Or is it perhaps that admitting bubbles exist would require them to make unpopular choices in policy?