The stock market has perked back up lately, with investors setting their past panic aside and pushing stock prices upward in a powerful rally. But that doesn't mean that stocks will stay up forever. The next downturn might be right around the corner.

More importantly, some companies never rebounded in the aftermath of the financial crisis. In trying to protect your money, how can you differentiate between general fluctuations in the market and permanent losses of capital?

Permanent capital loss: a definition
A permanent loss of capital occurs when a stock goes down because of deteriorating business operations and stays down for a very long time or even forever. For example, if a company files for bankruptcy protection, or its earnings power drops permanently, then shareholder value would also become permanently impaired. That said, here are some conditions you need to know about to avoid these dreaded losses.

Avoid leverage
Leverage magnifies gains and losses, and can make temporary setbacks permanent. Earlier in this decade, homeowners borrowed a lot of money that they couldn't afford, to bet on rising home prices.

Of course, in the long term, home prices will rise again. But now, prices have tumbled, and the surplus of inventory and lack of easy credit has left investors without any buyers for the real estate they purchased. Consequently, many investors who leveraged their purchases too heavily have been forced to give up their homes. Thus, this temporary downturn in the housing industry has become a permanent loss for many investors.

Countrywide Financial is a textbook case in which shareholders suffered a permanent loss of capital in large part because of excessive leverage. Founded in 1969, the company was renowned for its history of surviving brutal real estate and mortgage cycles and became the largest mortgage lender in the U.S.

However, Countrywide's nearly four decades of successfully navigating those cycles stopped dead in the water when excessive use of debt left it with an evaporating margin of error. Using a simple measure of leverage (assets divided by equity), the numbers (in millions) tell the tale:

 

1993

1997

2002

2006

Assets

3,299.1

7,689

58,030.7

199,946.2

Equity

693.1

1,611.5

5,161.1

14,317.8

Assets/Equity

4.8

4.8

11.2

14.0

Many factors contributed to Countrywide's downfall, but excessive leverage clearly played one of the largest roles in forcing Countrywide to sell itself at a low price to Bank of America (NYSE:BAC).

Avoid obsolescence
As new technology rolls in, outmoded ideas fade. The rise of the Internet made big winners out of popular online companies like eBay (NASDAQ:EBAY) and Amazon.com (NASDAQ:AMZN). But as this new method of obtaining data rapidly spread, Internet users abandoned newspapers. The loss of traditional newspaper readers might be permanent, and that has severely impaired the industry's earning power.

Shareholders who didn't anticipate the newspaper's gradual obsolescence and bought shares of New York Times (NYSE:NYT) at around $50 per share back in 2004 have probably suffered a permanent impairment of capital. Shares now languish at around $8 per share. Other newspaper publishers, such as Gannett (NYSE:GCI), have suffered similar declines.

Understanding where a company is in the life cycle of its industry is crucial for an investor. Companies that lose competitiveness to new technologies might never recover, and that dissolution will result in a permanent loss for investors who arrive too late to the party.

Avoid shrinking moats
In addition to leverage and obsolescence, a shrinking moat can also permanently impair shareholder value. Warren Buffett, chairman of Berkshire Hathaway (NYSE:BRK-A) (NYSE:BRK-B), purchased Dexter Shoe, a U.S. shoe manufacturer, in 1993. However, the shoe industry was in the process of being outsourced to Asia, where manufacturers using cheap labor could severely undercut domestic producers.

So even the best investors make mistakes, and Buffett later noted that purchasing Dexter was clearly a mistake on his part, because of its dwindling competitive advantages.

Beware of "bargain" stocks
Even after the big run-up, many stocks still have lost substantial ground over the past two years. Many investors are still sitting on some fairly large losses. Many of those stocks are down because of overall market volatility, and prices will eventually reverse as our economy strengthens over time. However, some stocks may be down for more reasons than just general market movement.

It's important for investors to distinguish how companies stand relative to these conditions, and whether the ones that are selling now are true values with the potential to rebound.

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Dan Caplinger updated this article, originally written by Emil Lee and published Jan. 22, 2008. Dan owns shares of Berkshire Hathaway. Amazon.com, Berkshire Hathaway, and eBay are Stock Advisor recommendations. Berkshire Hathaway and eBay are Inside Value picks. The Fool owns shares of Berkshire Hathaway. Try any of our Foolish newsletters today, free for 30 days. The Fool has a disclosure policy.