Prof Phelps writes in the FT
Swings in venture activity created a fluctuating economic environment. Frank Knight, observing US capitalism in his 1921 book, said that a company, in all of its decisions aside from the handful of routine ones, faces what is now called “Knightian uncertainty”. In an innovative economy there are not enough precedents to be able to estimate the probability of this or that outcome. John Maynard Keynes in 1936 insisted on the “precariousness” of much of the “knowledge” used to value an investment – thus the “flimsiness” of investors’ beliefs. (Yet now he is seen as “Smith plus psychological swings”.)
But why did big shareholders not move to stop over-leveraging before it reached dangerous levels? Why did legislators not demand regulatory intervention? The answer, I believe, is that they had no sense of the existing Knightian uncertainty. So they had no sense of the possibility of a huge break in housing prices and no sense of the fundamental inapplicability of the risk management models used in the banks. “Risk” came to mean volatility over some recent past. The volatility of the price as it vibrates around some path was considered but not the uncertainty of the path itself: the risk that it would shift down. The banks’ chief executives, too, had little grasp of uncertainty. Some had the instinct to buy insurance but did not see the uncertainty of the insurer’s solvency.
NNT calls this the difference between Mediocristan and Extremistan. Extremistan is where the Gaussian models breakdown. This is the world of Knightian unceratinty.