It's not impossible in a crisis for cascading numbers of derivative problems to unfold. Rising interest rates. Interest rates impact heavily the profits of publicly-held corporations. They also raise the cost of borrowing to invest. High rates historically choke off speculation.
Investors erroneously believe they can get out of the market ahead of any major downturn.
It's taken almost 20 years for investors to pour this much money into the stock market. If they should head for the exit in a panic or disorder, there is no way for the majority to get out smoothly. Many people believe that closing trading will keep the market from plunging and restore calm in a steep decline. Once the averages drop ten percent, the market closes for an hour. Booms are followed by busts and credit expansions end in credit contractions, recessions, and depressions.