Here is a funny thing about valuation “bubbles” involving financial instruments. In every individual case, you unavoidably end up asking: "What were they thinking?” Or stated differently, what causes a significant part of the supposedly rational investing public to collectively lose their minds for a relatively brief period? A few tulip bulbs, for example, were valued more highly than a modest Amsterdam house in 1637, until they weren’t. Leveraged speculation in frontier commodity markets of Asia and America led to...