Here's what happens during a mob panic, like the one today on Wall Street. The mob behaves irrationally, doing the exact opposite of what each individual member of the mob would do if he or she stopped for a minute to think.

OMG, said the media all weekend after Standard and Poors reduced Uncle Sam's credit score on Friday evening, the stock market will crash on Monday! And it did.   US debt, also known as bills, notes and bonds, became riskier investments because of S&P's pronouncement the US was less capable of paying its debt than it had been before.

Now, what is a stock market crash? It's what happens when most of the people in the market want to sell. To make the sale, they have to take less for the stock. Supply and demand. No Nobel Prize in economics needed.

But what did those panicked sellers do with the money they got in return for their devalued stocks? They purchased US debt with it! Oy!