How 'animal spirits' move the stock market

She pulled out of the market in 2005 because she was tired of the ups and downs, and she has no plans to invest in anything again except real estate.

"I would like to invest in the future, but it's so volatile, I don't know that I would," said Hritz, 50, an ultrasound technician in Chardon, Ohio. Hritz submitted her story to CNN's iReport.com.

Hritz is just one example of an American who has lost confidence in the stock market, which has plummeted in recent months. Confidence among investors as a whole is a key factor in determining how the market behaves, economists say; when investors collectively lose confidence in the market, it is more likely to drop.

In fact, confidence is an example of an "animal spirit," a term referring to the psychological factors that move the market. British economist John Maynard Keynes coined the term.