The thing that got me most about Federal Reserve Chairman Greenspan's warning about "irrational exuberance" of the markets was that the warning was in 1996, and it seemed to me and many others already obvious by then, and that Greenspan was cautious and late in his warning.

Yet, the markets continued rapidly upward for another FOUR years. Shorting the high-flying stocks with negligible income in 1997 or 1998 would have been completely sensible. And it would have wiped you out, as you would have been years too early.

It just proves the adage: "The markets can remain irrational longer than you can remain solvent."

Today, the levels of (over-)investment compared to investment are even more extreme. But when is the time to call it?