In 1929, Irving Fisher was a prominent economist who was convinced that financial markets would always know best. His thinking articulated the theory that financial markets would always have an underlying sense of rationality and stability, and would basically find equilibrium by themselves. His theories of course were refuted during the Great Depression of 1933. But to add insult to injury, decades later scholars, investors, and government officials repeated precisely the same mistake by trusting in rational markets, resulting in the global economic meltdown that we are now facing. The take away lesson from this is very simple — there is no such thing as a rational market.