The Internet may prove to be the greatest human invention of all time. Investing in Internet companies in 2000, however, may prove to have been one of history's greatest follies.

Yet 2000 was a heady year for Internet investment. Guides such as Greg Kyle's 100 Best Internet Stocks to Ownshowed you "how to get in on this once-in-a-lifetime opportunity." Kyle predicted that there would be 430 million Internet users by 2003, and that by 2005, "consumers will spend $150 billion shopping online."

In fact, those estimates proved conservative. By 2003, nearly 600 million people were online. In 2005, shoppers spent more than $175 billion on the World Wide Web.

Time to cash in
But even though Internet usage blew away expectations, you would have been a big loser if you'd invested in Kyle's 100 best Internet stocks. How much of a loser?

In the fall of 2007, we spent hours computing the returns figures. Spoiler alert: The results are painful.

Had you invested $1,000 in each of Kyle's 100 Internet names back on April 20, 2000, and held them through September 2007, your $100,000 investment would have turned into -- drum roll, please -- $37,814. That's a total return of negative62%, and again, that return is through the fall of '07 -- beforethe current bear market.

You were more likely to pick a company that would go bankrupt (18) as you were to pick a company that simply increased in price(13)!

To the moon!
And that's despite some successes. AXENT merged with Symantec (Nasdaq: SYMC), and a $1,000 investment there would have been worth more than $4,600. Auctioneer king eBay (Nasdaq: EBAY) would have doubled your money over the same time.

You also would have done quite well buying Expedia (Nasdaq: EXPE), getting merged into IAC/InterActiveCorp (Nasdaq: IACI), and then getting shares of both when Expedia was spun back off.

But even those winners can't change the fact that 18% of Kyle's companies went bankrupt. And many of the companies that survived, including Yahoo! (Nasdaq: YHOO), Priceline.com (Nasdaq: PCLN), and RealNetworks (Nasdaq: RNWK), declined by 60% or more.

What went wrong -- and why
Most of the companies profiled in the book were profitless -- and burning through capital at a rapid rate. Indeed, many of the companies shouldn't have been worth a dime ... let alone billions of dollars.

See, Internet companies at the turn of the century were expected to generate massive cash profits. They didn't. A stock's value is nothing more than an estimate of its ability to generate cash profits over time. Before long, "market share," "network effects," "eyeballs," and "B2B business models" were exposed as Northern California euphemisms for "no cash."

The value of valuation
That's why valuation is such a critical component of investing. As the Internet mess illustrates, taking a top-down investing approach -- starting with the best, fastest-growing industry-- will usually lead to failure. Show us that industry and we'll find you a stock operating therein that's going down in flames.

That's why we advocate a bottom-up investing approach. Start at the company level and work up from there.

It's also why there are no no-brainers in investing. Just to repeat: Although the Internet has been even more successful than Kyle imagined, the stocks he profiled were mostly disasters.

China = the new Internet
When an earlier version of this article was published, we made the case that the lesson of the Internet was as timely as ever -- and not because of the burst housing bubble. Why was it timely? China. Continued...