Stocks fell by so much they tripped a circuit breaker shortly after trading started
This is not unprecedented. Far from it. During the Great Depression, on "Black Monday in 1987" and during the Great Recession, stocks fell by much more.
That's not exactly a comforting thought.. .but it helps put today's 6% decline in context.
10/19/1987 -20.467%
10/28/1929 -12.34%
10/29/1929 -10.16%
11/16/1935 -10.11%
03/18/1935 -10.06%
10/15/2008 -9.03%
The S&P 500 fell by more than 7%, halting trading for 15 minutes.
The next circuit breaker would be if the market falls by 13%. That would pause trading for another 15 minutes.
If the market plunged 20%, everyone would go home: Trading would stop for the day.
Circuit breakers pause and ultimately halt trading to avoid a repeat of "Black Monday" on October 19, 1987, when the Dow crashed 22.6% in a single day.