Since October 9th, the NASDAQ’s low point of the past three years, Amazon.com, eBay, and Yahoo have jumped an average of 155%. Does that mean you ought to buy them? If they continue at their blistering pace this year, Yahoo will end the year up 181%, eBay 124% and Amazon 192%. So, should you rush out to buy them?

Only if you didn’t learn your lesson the first time around.

Amazingly, this is the same nonsense we saw in the late 1990s. At the height of the dot-com craze, tech stocks rose to unprecedented highs. Then the bubble burst, and those stocks came tumbling down. By the end of 2001, Amazon.com had fallen 96 percent from its high. eBay was down 87% and Yahoo crashed 97%. By 2001, it was clear that the ’90s were over.

Now, it seems as if the ’90s are back, because investors, for some strange reason, have bid up the price of these same stocks. Apparently, investors have learned nothing from the past three years.

Long-time readers of this newsletter — and all our clients — know that we spent much of our time in the late 1990s warning people not to invest in tech and Internet stocks. Many ignored us, to their regret.

One big source of concern was the price-to-earnings ratio, called P/E. The lower the P/E, the cheaper the stock. Historically, the overall stock market trades at a P/E of 15 to 18; the market crashed in 1987 when the market’s P/E reached 27.

Yet, at the height of Internet Mania in 1999, Yahoo’s P/E was 4,326 and eBay’s was 3,127. Amazon.com didn’t even have a P/E, because it never had a profit! Many investors wondered why those stock prices fell; what they should have asked was how those prices ever rose so high in the first place, because there was no legitimate reason for such lofty stock prices. The P/E predicted the dot-coms would fall, as did many other factors.

And so, in the end, things worked out as they always do: By returning to normalcy. Thus, in the post bubble 2000s, we can look back on the late 1990s as a period of investor insanity, a time when investors lost all logic and reason and willingly paid absurd prices for stocks that were then trading at unsustainably high P/E ratios. Certainly, those days are gone forever.

Or are they? Based on their recent performance, Yahoo’s P/E is 110, eBay’s is 112 and Amazon still is yet to make a profit.

Here we go again.

Do yourself a favor, and stay away from investments like these. Maybe you didn’t listen to my advice in the 1990s. Here’s an opportunity to learn from your mistakes.