I did state that an exogenous shock could take the market by surprise and, in a sense, it got one on Monday. Atlanta Fed President Dennis Lockhart stated in a speech to the Rotary Club of America that he supported "similar tapering steps" as the one taken last month by the FOMC (reducing asset purchases by 10 billion dollars). Almost as the words left his mouth the market started its swoon right into the close of trading.
Obviously his remarks (which were not anything that anyone didn't already know) on top of a very weak employment report the previous Friday were the catalysts for the sell off. Here's a five minute chart of the S&P inclusive of Friday's (1/10) and Tuesday's (1/14) price action: