Yikes! For millions of American savers and investors, it has been a terrifying month.

They've watched their shares, bonds and mutual funds crash almost across the board. Many people, understandably, are panicking and fighting the urge to sell. The market's swings have been violent.

It's at times like this that you realize, with apologies to Yogi Berra, that 90% of this game is half mental.

Managing your investments is one thing. Managing your emotions during the biggest financial panic in a generation is another.

Knowing history, as well as finance, is a big help. Here are 10 things to help keep matters in perspective:

1 We have been here so many times before. Of course you know about the famous crashes of 1929 and 1987.

But what about the panics, crashes and slumps of 1812, 1837, 1857, 1873, 1903, 1907, 1914, 1917, 1930-2, 1937, 1946, 1962, 1966, 1973-4, 1976-8 and 1998? Not to mention, of course, the dot-com bust and market slump of 2000 to 2003.

These things happen quite often. Some are worse than others. But the market has always, eventually, recovered.

2 You think this is bad? During the Great Depression, share prices fell about 90%.

At the lows, recounts historian Ron Chernow in "The House of Morgan," members of the Union League Club in New York wallpapered a room with stock certificates rendered almost worthless. A few years later, the market had recovered sufficiently that some members asked for the certificates back.

3 In August 1998, the Dow Jones Industrial Average fell 1,000 points -- about one fifth -- in a few days, following the financial crisis in Asia and Russia. Despite the dire warnings, the U.S. didn't enter a severe recession. Most people have even forgotten there was a panic in 1998.

4 It wasn't the crash of 1929 that caused the Great Depression. Wall Street actually rallied sharply in the following six months.

It was a string of subsequent policy blunders that caused most of the misery. Economic knowledge in the 1930s, like medical knowledge in the Victorian Age, was rudimentary, and often did more harm than good.

5 You think this is bad (Part II)? In the early 1970s the London stock market collapsed by about three quarters; a string of banks failed, and the financial crisis threatened the economy and political stability.

At the lows, a leading financier told a London audience that their best "investments" would be cans of food, gold coins "and a gun." A few months later, the stock market began booming again and prosperity returned.

6 Yes, the economic fundamentals may look ominous. Debt levels are high, wages are flat, and so on. But as Dan Bunting, a veteran British fund manager, likes to point out: "The economic fundamentals always look terrible."

7 Stock-market panics were once so common that, according to 19th-century Wall Street manager Henry Clews, some investors living in the countryside grew very rich simply by waiting for the crashes and then scooping up stocks.

These gentlemen, Mr. Clews recalled in his memoirs, only appeared in New York during a panic. They sold their stocks again at huge profits when the market had recovered, and then returned to their country estates to await the next crash.

The nation prospered nonetheless.

8 Certainly it was a surprise to lose Bear Stearns, Lehman Brothers, Washington Mutual and Merrill Lynch (sort of).

But in 1873 so many banks and brokerage houses failed, and so many others had to shut their doors temporarily, that the stock exchange itself closed for about 10 days to stop the panic.

9 Anyone who bought after the crash of 1873 and held on for 20 years, simply reinvesting dividends, trebled his money.

Anyone who did the same following the gigantic crash of 1907, when J.P. Morgan Sr. stepped in to rescue the financial system, made a 700% return. After the 1987 crash, the figure was 900%.

Even someone who invested after the crash of 1929 and held on for 20 years eventually doubled his money, despite the disasters of the Great Depression and World War II. (Thanks to Global Financial Data for the historical calculations.)

10 Anyone with shattered nerves could do worse than spending $20 on Fred Schwed's hilarious investment classic "Where Are The Customers' Yachts?" It was written in 1940, and it's still right on the money.

"When there is a stock-market boom, and everyone is scrambling for common stocks, take all your common stocks and sell them," he wrote. "Take the proceeds and buy conservative bonds."

If shares keep rising, don't worry: Just wait for the market to crash. It will. When that happens, and "the panic … becomes a national catastrophe, sell out the bonds (perhaps at a loss) and buy back the stocks."

Hold them until the next boom. "Continue to repeat this operation as long as you live, and you'll have the pleasure of dying rich."

No, it's not quite as simple as that. But as Mr. Schwed knew, you're better off buying stocks when nobody wants them and their prices are cheap than when everybody wants them and the prices are dear.

Or, in a nutshell: Never get too bullish -- and never get too bearish.

Write to Brett Arends at brett.arends@wsj.com