Back in the late 1960s and the early 1970s, investors went gaga over 50 large-cap blue chip stocks called the Nifty Fifty. These equities were often described as “one decision” trades that you bought and kept for life.

At their peak, the NIfty Fifty were trading at 42 times earnings — more than twice the S&P 500. Among the storied names were icons of American business like Polaroid, Xerox, Coca-Cola, General Electric, Sears and Texas Instruments. Some of these stocks remain viable businesses today, but since the start of this century, none of these names have been anything but terrible investments.

The Nifty Fifty stands as a historical warning to generations of investors of the heavy price to pay for unbridled, uncritical enthusiasm.

At their peak, the Nifty Fifty comprised almost all the gains of the S&P 500, and if that fact sounds eerily familiar … that’s because today’s Nifty Fifty are the ‘FAANG’ stocks, plus “M.” That is, Facebook, Apple, Amazon, Netflix, Google parent Alphabet and Microsoft.

Just like the Nifty Fifty of yore, the “FAANG” stocks are dominant companies of their day. They touch every aspect of our lives — often several times per day. There is no doubt that these are very good businesses that may last for decades.

Or maybe not.

That’s the point of the Nifty Fifty that investors should never forget. After they had their parabolic rise, the Nifty Fifty then proceeded to dive and lose more than half their value in the ensuing bear markets of the mid-1970s. By 1975, investors who bought the Nifty Fifty at their peak in 1972 would have seen more two-thirds of their wealth evaporate.

Now, as professor Jeremy Siegel of the Wharton School pointed out in a very popular 1996 white paper, those investors who had the patience to hold on until 1988 would have recovered all of their losses, and furthermore would have matched the returns of the S&P 500. Although that recovery sounds impressive, it’s actually mainly due to just one stock: Philip Morris. Absent that one single holding, the Nifty Fifty would have been a disaster of a portfolio.

Furthermore, professor Siegel’s study benefits from its end date. If we were to carry on the thought experiment to present times such stocks as Coca-Cola and GE, which looked so promising in the late 1980s, have been nothing but dogs as investments ever since.

In many ways, the FAANG phenomenon is even more dangerous than the Nifty Fifty. The Nifty Fifty were at least somewhat diversified by industry and by name (and as Philip Morris shows, just one lucky position kept the whole portfolio alive).

The “FAANG plus M” stocks, on the other hand, are woefully concentrated by both size and industry and therefore could be vulnerable to a massive sell-off the moment they hit their natural limits of growth.

Ultimately, the lesson of the Nifty Fifty is that a company is not its stock.

It may have a wonderful, viable business for many years to come, but the natural competition of the marketplace makes it extraordinarily difficult for any company to remain dominant for perpetuity. That’s why valuation matters.

Ultimately the thrill of the gain gives rise to the agony of the loss and those investors who are unabashedly bullish on the current crop of superstar stocks would be wise to learn their stock market history.