Forget the dot-com boom with its "irrational exuberance" and the real estate bubble that was supposed to be invincible: Current market sentiment eclipses all of that.
In fact, bullishness has never been this high going all the way back to 1987.
That's through three rousing bull markets, a couple of crashes, the "Great Moderation" of the 1990s and all sorts of other history-making events. A market that was supposed to flounder this year under a new president instead has taken off, and investors are pumped.
Bullishness is at 63.1 percent of market professionals responding to the latest Investors Intelligence survey. That's the highest level since the year of the infamous "Black Monday" Oct. 19, 1987, crash that sent the U.S. market down nearly 23 percent in one day.
All the optimism comes with the market setting a succession of new highs, including trading Wednesday that pushed major averages up more than 1 percent across the board.
"You can totally understand why this is where it is considering the market action," said Nick Colas, chief market strategist at Convergex. "What's hard about interpreting it against 30 years of history is you have a very unusual period in economic and political history now, so you have to throw out the usual rulebook."
The Trump bump now a bull rush
Indeed, the market's fortunes of late have been tied to growth hopes that President Donald Trump has brought.
Wednesday's rally came a day after Trump delivered what was widely considered an on-message litany of accomplishments and plans for the future. While the speech to a joint session of Congress offered little economic detail beyond previously disclosed plans to direct $1 trillion to infrastructure projects and boost military spending, the president's sharp — and perhaps unexpected — focus on universal issues appealed to Wall Street and gave another leg to the post-election rally.
"In the near term, equities are fine because there's a lot of enthusiasm behind it. Is it sustainable? That's the ultimate question," Colas said. "It depends 100 percent on what happens in Washington, how much of the Trump agenda gets through and at what speed."
Typically, sentiment surveys are used as contrarian indicators. Bullishness above certain levels — certainly at 30-year highs — often would be seen as selling opportunities.
In the Investors Intelligence survey, a reading above 55 percent typically would trigger a warning to take profits, said II editor John Gray.
However, investors don't seem to be in any hurry to sell, particularly considering that the Trump presidency is just getting started.
"My first reaction is it makes me very nervous. It is always a great contra indicator when enthusiasm is too high or pessimism is too low, so it does concern me," said Michael Yoshikami, CEO of Destination Wealth Management. "The difference between this and the dot-com bubble is while valuations are probably stretched, I don't think they're so far off that you can necessarily say it's irrational exuberance. I would say it's more pure exuberance."
Dark lessons of history
The "irrational exuberance" reference, of course, goes back to former Fed Chair Alan Greenspan, who in 1996 warned, four years before a new bear market, that equity values could be stretched.
Yoshikami doesn't think the current "exuberance" is reason to ditch stocks, even though he believes a 10 to 15 percent correction this year is a strong possibility. Rather, he advocates more toward getting defensive, buying neglected sectors like pharma that haven't participated in the latest stretch of a bull market just days away from its eighth anniversary.
"Five percent (down) is kind of a given on any given day. A 10 to 15 percent drop could occur. In fact, I would actually be surprised if it did not occur this year, which is not to say I'm negative on equities," he said. "There's still a lot of buying pressure kind of sitting on the sidelines."
One of the biggest looming shadows over the market now is valuation.
Using the Robert Shiller cyclically adjusted PE comparison, which weighs price against earnings of the past 10 years, stocks are trading at highs seen only twice before — around the onset of the 2000 bear market and, even more ominously, the 1929 market crash that ultimately led to the Great Depression.
"In the short term, I'm not worried. In the longer term, absolutely, this scares the heck out of me," said Brad McMillan, CIO at Commonwealth Financial Network. "The only other time we've come close [to this CAPE level] was 2007. Every time we've been at or above the current level, we've seen a significant market pullback."
However, he also doesn't think it's time to sell.
In fact, times of elevated sentiment in either direction — like the heady bull market days in 2007 or the panic in early 2009 — call most for investors to keep their heads.
"Right now there's no reason to panic," McMillan said. "We're moving into a moment that could be equivalent to boom times, and that's wonderful and it feels great. But it also raises the risks. You have to be cautious of those risks even as you're enjoying the good times."
This article originally appeared on CNBC. Read more from CNBC: