Green Mountain Coffee Roasters (Stock Symbol: GMCR) just showed how momentum works both ways in the stock market. Its shares are the latest to crash down from a nosebleed trading multiple, after the company grew less than analysts expected.

Dendreon (Stock Symbol: DNDN) was decimated today, August 4, 2011 after the company’s second-quarter results fell well short of Wall Street expectations on disappointing sales of its Provenge prostate cancer drug.

After the stock market crash on October 19, 1987, both individual and institutional investors were asked about their “Investor Psychology” on “Black Monday” and what triggers kept them in or out of the market that day.