Keynes via Robert Skidelsky.
The basic question Keynes asked was: How do rational people behave under conditions of uncertainty? The answer he gave was profound and extends far beyond economics. People fall back on “conventions,” which give them the assurance that they are doing the right thing. The chief of these are the assumptions that the future will be like the past (witness all the financial models that assumed housing prices wouldn’t fall) and that current prices correctly sum up “future prospects.” Above all, we run with the crowd. A master of aphorism, Keynes wrote that a “sound banker” is one who, “when he is ruined, is ruined in a conventional and orthodox way.” (Today, you might add a further convention — the belief that mathematics can conjure certainty out of uncertainty.)
But any view of the future based on what Keynes called “so flimsy a foundation” is liable to “sudden and violent changes” when the news changes. Investors do not process new information efficiently because they don’t know which information is relevant. Conventional behavior easily turns into herd behavior. Financial markets are punctuated by alternating currents of euphoria and panic.
From the NYT.