“Irrational exuberance is the psychological basis of a speculative bubble,” wrote Yale economist Robert Shiller in his 2000 book - Irrational Exuberance.

“I define a speculative bubble as a situation in which news of price increases spurs investor enthusiasm, which spreads by psychological contagion from person to person, in the process amplifying stories that might justify the price increases, and bringing in a larger and larger class of investors who, despite doub...