This article's headline, a direct quote from Berkshire Hathaway (NYSE:BRK-A) (NYSE:BRK-B) Vice Chairman Charlie Munger, cuts right to the heart of the matter: If you are not investing based on fundamental valuation principles, you are not investing. You may think you are, but Ben Graham had another term for it: speculation.

Intelligent investing defined
As Graham stated in the book Security Analysis: "An investment operation is one which, upon thorough analysis, promises safety of principal and a satisfactory return. Operations not meeting these requirements are speculative." Graham's definition implies that a true investment is made only when you have the right data and reasoning, followed by a suitable price that ensures a margin of safety. Putting capital to work any other way is, by its nature, speculative.

Value investors focus not on their performance in a bull market, but on their perseverance during a bear market. In his 1961 partnership letter, Warren Buffett expressed this crucial point when he told his partners, "I would consider a year in which we decline 15% and the [Dow Jones] average 30% to be much superior to a year when both we and the average advanced 20%." Most investors don't fully grasp this investing approach, and the result is inferior long-term performance relative to the benchmarks.

Dealing with bear markets
In the 1960s, Buffett invested more than 30% of his assets in one company, American Express (NYSE:AXP), during that company's worst scandal. While everyone else was running, Buffett stood still, because he was confident in his data and reasoning.

Now, Buffett has done the same thing. When companies like General Electric (NYSE:GE) and Goldman Sachs (NYSE:GS) were having trouble finding capital at any price, Buffett was there -- with a deal that could turn out very well for shareholders if anything but the worst-case scenario happens.

Always remember that price is what you pay and value is what you get. A fantastic business like Google (NASDAQ:GOOG) is undervalued at one price, fairly valued at another, and overvalued at yet another. Two years ago, investors in Google were sacrificing a margin of safety and betting on the continuance of very high growth rates, which we know simply cannot go on forever. Now, though, the stock may be more of a bargain at roughly half its late-2007 price.

When you bet, bet big
Few words carry more weight than these:

Truly outstanding investment opportunities occur only occasionally. In general, the better they are, the rarer they are. Such opportunities are normally long-term in their maturation and by careful study can be foreseen long before they come to the attention of most investors. ... The very highest profit potentials occur whenever there is a convergence of two or more primary causes.

These sound like homespun words of wisdom from Graham or Buffett, but they aren't. They come from silver analyst Jerome Smith in his book Silver Profits in the Seventies, published more than 30 years ago. Smith was referring to silver, but his words also characterize the qualities of superior investments that true value investors seek to exploit.

Smith is right: Really good investment ideas are rare. So when you find one, bet big. If your thorough analysis is correct and the price is right, you should have no hesitation in investing heavily. That's one reason why Buffett has taken such large positions in the stocks he buys, including a more than 20% stake in Burlington Northern Santa Fe (NYSE:BNI).

Simply put, if your convictions won't allow you to put 10% of your assets in one investment, you probably don't need to have even 1% of your assets invested. But that's why such obvious investments are so rare, and when your data and reasoning are correct, be sure to take advantage of the opportunity.

Buying good businesses at bargain prices allows the investor to ride out a storm relatively unscathed. But sound investing is not easy. The key is to train yourself to be unemotional about the market and maintain an unwavering level of discipline. History has shown that there will always be periods of prosperity followed by periods of economic contraction. That will never change. If you invest with the aim of keeping your capital, the upside will take care of itself.

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This article, written by Sham Gad, was originally published on July 27, 2007. It has been updated by Dan Caplinger, who owns shares of Berkshire Hathaway. American Express and Berkshire Hathaway are Motley Fool Inside Value recommendations. Google is a Motley Fool Rule Breakers recommendation. Berkshire Hathaway is a Motley Fool Stock Advisor selection. The Fool owns shares of American Express and Berkshire Hathaway. Try any of our Foolish newsletters today, free for 30 days. The Fool has an intelligent disclosure policy.