TEN YEARS AFTER the weekend that upended the financial world, its most important lessons lie not in what has changed, vast and profound though that is, but in what hasn’t changed. The main causes of the last crisis—human self-delusion and irrationality—will be the main causes of the next one. If that seems unbearably depressing, cheer up: It tells us what to watch out for.
Lehman Brothers’ bankruptcy announcement in the predawn darkness of Sept. 15, 2008, wasn’t the first or worst event of the financial crisis, but it was the most frightening because it was unthinkable, given the investment bank’s size and exalted stature. It unmoored us from our certainties and set the stage for other disorienting changes, many of which are now embedded in our daily lives.
But those same certainties were built on foundations that turned out to be unfounded. We all knew that U.S. homeownership rises over the long term; that’s part of what America is about. That unshakable confidence helped fuel the easy-credit home-buying frenzy of the early 2000s, a frenzy driven by the belief that an unprecedented spike in property prices would last indefinitely. Big institutional investors—including Lehman—bought into the faith-based rally, betting on the kinds of shaky subprime loans that eventually brought them down and cratered the economy. (As for the homeownership rate, it plunged, erasing 40 years of increase, and is nowhere near recovering.)
If delusional optimism led to widespread financial harm, delusional pessimism has kept many Americans from healing.
We’re still less likely to own stocks than we were even after the dotcom meltdown of 2000–01, says the Gallup research firm. More of us are truly terrified of anything associated with finance, which makes us behave bizarrely. A new survey by the Betterment robo-advisory firm finds, incredibly, that 48% of respondents think the stock market hasn’t gone up in the past decade, including 18% who think it has gone down. That’s half of American adults, and it would take them 10 seconds online to learn that stocks are up 140% since Lehman failed. But they don’t look. They’re like the person who can’t open the letter from the IRS. The very thought makes them quiver.
Such self-destructive behavior reminds us of what we relearned in the crisis: Most people don’t behave rationally. Too many on Wall Street believed the madhouse markets reflected people making the machinelike calculations of classical microeconomics. Former Federal Reserve chairman Alan Greenspan, a hyperrational libertarian for 40-plus years, confessed before a congressional committee he was “shocked” that his model of “the critical functioning structure that defines how the world works” didn’t work. He wasn’t alone.
The most damaging irrationality was a dogged but mistaken belief that fundamental rules of valuation no longer applied—that this time is different. The phrase became the title of a bestseller by economists Carmen Reinhart and Kenneth Rogoff, showing that such a belief has fueled financial disasters for centuries. Deep-rooted errors identified by behavioral finance— overconfidence, over-extrapolation, drawing big conclusions from small samples—reinforced the misjudgment.
No one knows what will trigger the next crisis, but we know for sure it will be built on the same kind of mistakes. Don’t count on employers, banks, insurers, or regulators to protect you. But you can shield yourself because you already know how to spot trouble. Specifically:
- Ask yourself regularly which markets look reasonably priced only if you believe that fundamental rules of valuation no longer apply. To help you identify such hotspots…
- Listen to the responsible fringe—thinkers with strong records who are contradicting the mainstream view. Last time they included fund manager Jeremy Grantham and economists Robert Shiller and Nouriel Roubini. You can’t know if they’re right, but you can prepare for the possibility that they might be. That means…
- Don’t predict the future—you can’t. Instead, envision scenarios and plan for each one. Don’t worry that most of your plans will be wasted; it’s better to be prepared for events that don’t happen than unprepared for those that do.
The crisis that erupted 10 years ago reminded us that even in a worldwide financial calamity, not everyone suffers equally. Hedge fund manager John Paulson made billions betting against subprime mortgages, a business that had abandoned usual valuation rules. You may not do so well, but we know that some people will come through the next crisis just fine. Resolve, rationally, to be among them.
A version of this article appears in the October 1, 2018 issue of Fortune with the headline “How to Spot the Next Financial Crisis.”