Less understood is the mass psychology of the speculative mood.

A Short History of Financial Euphoria by John Kenneth Galbraith.  Page 4.

Less understood is the mass psychology of the speculative mood. When it is fully comprehended, it allows those so favored to save themselves from disaster. Given the pressure of this crowd psychology, however, the saved will be the exception to a very broad and binding rule. They will be required to resist two compelling forces: one, the powerful personal interest that develops in the euphoric belief, and the other, the pressure of public and seemingly superior financial opinion that is brought to bear on behalf of such belief. Both stand as proof of Schiller's dictum that the crowd converts the individual from reasonably good sense to the stupidity against which, as he also said, "the very Gods Themselves contend in vain."

Although only a few observers have noted the vested interest in error that accompanies speculative euphoria, it is, nonetheless, an extremely plausible phenomenon. Those involved with the speculation are experiencing an increase in wealth-getting rich or being further enriched. No one wishes to believe that this is fortuitous or undeserved; all wish to think that it is the result of their own superior insight or intuition. The very increase in values thus captures the thoughts and minds of those being rewarded. Speculation buys up, in a very practical way, the intelligence of those involved.