There is protection only in a clear perception of the characteristics common to these flights into what must conservatively be described as mass insanity

A Short History of Financial Euphoria by John Kenneth Galbraith.  Page 1.

That the free-enterprise economy is given to recurrent episodes of speculation will be agreed. These - great events and small, involving bank notes, securities, real estate, art, and other assets or objects - are, over the years and centuries, part of history. What have not been sufficiently analyzed are the features common to these episodes, the things that signal their certain return and have thus the considerable practical value of aiding understanding and prediction. Regulation and more orthodox economic knowledge are not what protect the individual and the financial institution when euphoria returns, leading on as it does to wonder at the increase in values and wealth, to the rush to participate that drives up prices, and to the eventual crash and its sullen and painful aftermath. There is protection only in a clear perception of the characteristics common to these flights into what must conservatively be described as mass insanity. Only then is the investor warned and saved. 

 

There are, however, few matters on which such a warning is less welcomed. In the short run, it will be said to be an attack, motivated by either deficient understanding or uncontrolled envy, on the wonderful process of enrichment. More durably, it will be thought to demonstrate a lack of faith in the inherent wisdom of the market itself.