These are scary times for investors trying to shore up their retirement portfolios. Stocks' values are down, inflation is ticking up and home prices are sliding. But as investors nervously eye all that, they may be overlooking the biggest threat of all: themselves.

"How you react to negative news about the markets can do far more damage to your retirement portfolio than temporary trends in the market," says Mark Cortazzo, an investment adviser at Macro Consulting Group in Parsippany, N.J. "Investors can truly be their own worst enemies."

While investors are prone to making mistakes no matter which direction the market is headed, when stocks lose value -- as they have for four consecutive months -- investor errors can have more exaggerated effects on wealth, Cortazzo says.

So how much damage does the average investor inflict upon himself in real numbers?

At the request of Barron's, Christopher Cordaro, an investment adviser in Chatham, N.J., with Regent Atlantic Capital, ran some calculations to answer this question, and the answer isn't pretty.

Bottom line: Simply by making three of the most common errors -- failing to diversify wisely, trying to time the market and overpaying on investment expenses -- you would have missed out on $375,000 of gains

NEW YORK (AP) -- With a deal in place to save Bear Stearns from bankruptcy, the company's shares traded above the offer price Monday even as investors began turning a critical eye to other investment banks amid worries about how far the credit contagion could spread.

Despite the weekend agreement for JPMorgan Chase & Co. to buy Bear Stearns for a fraction of its value last week, worries that other banks had sizable exposure to troubled credit markets sent global markets tumbling. The uncertainty was evident on Wall Street, where the Dow Jones industrials sank by more than 100 points.

At Bear Stearns' 47-story headquarters in midtown Manhattan, many employees said they still couldn't believe that the nation's fifth-largest investment bank is -- essentially -- out of business. Employees said there was no meeting to inform employees about what was happening.

"It's my first job out of school. I thought it was a big company -- it would be good experience," said Ki Byung, who works for a division of Bear Stearns. "Now after a couple of months something like this happens."

Instead of making money, Bear Stearns employees trudged boxes of their personal belongings out of the investment bank while JPMorgan managers filed into it for the first time from that bank's headquarters directly across the street. While no layoffs have been announced, analysts expect that they could be