Dow 20,000 was ushered in with great fanfare. Traders on the New York Stock Exchange sported “Dow 20,000” hats. Even President Donald Trump joined the celebration.

Trump told ABC News he was “very honored” that the stock market gave his presidency a symbolic vote of confidence. “Now we have to go up, up, up. We don’t want it to stay there,” he said.

Everyone loves a bull market. Expecting stocks to go up forever, however, is a dangerous mindset to have as an investor. Recent history suggests that major milestones for the Dow should be viewed less as cause for celebration and more as warning signs.

What 1999 Can Teach Us About 2017

A case in point: Dow 10,000. On March 29, 1999, the Dow Jones Industrials closed above 10,000 for the first time ever.

The financial media, of course, cheered the milestone, feeding the public Wall Street propaganda rather than healthy skepticism.

Sure, the perma-bulls will always concede, there might be a pullback at some point. But books like Dow 36,000, released in 1999, bolstered the conventional wisdom that stocks were destined march higher over the next decade.

In fact, stocks went nowhere for 11 long years. The Dow suffered two crashes – one in 2002 and a bigger one in 2008.

In mid 2010, the blue chip average was right back where it was on March 29, 1999. The Dow crossed back above 10,000, as it had dozens of times before, to little fanfare.

It turned out to be the 10,000 cross that mattered. Finally, more than 11 years after the Dow first hit 10,000, stocks were in a new bull market. The Dow was on its way to 20,000.

Anyone thinking of buying stocks at today’s lofty valuations would be well advised to take heed of what happened to investors who bought at Dow 10,000 in 1999 and held on through today.

Yes, they did double their money (before dividends) in nominal terms.

But in real terms, the Dow hasn’t made any progress.

Investors would have been better off selling stocks when the Dow hit 10,000 and using the proceeds to purchase gold bullion.