If you could follow your ancestry back 2,000 years, you would be impressed. You come from a bright and tough stock of humans. That might be surprising if you’re a 90-pound weakling–or if you dine 7 days a week on fatty fast food. But make no mistake. Your lineage was awesome.

Weaker and less intelligent bloodlines died out. Yours didn’t. Yours were strong, smart and lucky enough to attract mates, reproduce, and care for their offspring. They also noticed patterns. If a massive tiger ate one of their friends, they were smart enough to avoid big tigers. If a grizzly bear wanted to eat them for lunch, they had to know how to fight–or run faster than their friends.

They found patterns to survive. Such pattern-seeking tendencies are now part of our DNA. But what was helpful back then is like a poison berry today –especially for investors. We seek financial patterns. If certain stocks or sectors soar, we think they’ll keep rising. When sectors fall or flat-line, we run away in fear. Jason Zweig explains this neurological science in his excellent book, Your Money And Your Brain.

Some time periods, however, are deadlier than others. We’re in one now. Almost everyone is making bucket loads of money, much as they did in the
mid-to-late 1920s and the late 1990s. During those times, reckless investors earned the greatest spoils. They bought stocks on borrowed money. They failed to diversify. During the late 1990s, they stuffed their portfolios with popular tech stocks. For a while, such investors earned blistering returns. But when those blisters popped, they gushed the most blood.

Before such bursts, they mistook luck for genius. That’s happening again now. When investors gamble on what’s popular, and they end up winning big, it’s often a sign there’s a scary time ahead. Hip stocks, for example, are rarely the biggest winners. But when hip household stocks reach stratospheric levels, it’s time for healthy fear.

For example, a $10,000 investment in Apple, five years ago, would have grown to $25,206 by January 12, 2018. If it were invested in Tesla, it would have soared to $102,165. If it were invested in Netflix, it would have rocketed to $152,870. And these were just five-year gains on a $10,000 investment!

In 2017, almost everyone made money. Over just 12 months, the S&P 500 gained 21.83 percent. International stocks soared 27.19 percent. Technology stocks, tracked by iShares US Technology ETF (IYW) jetted to 36.61 percent. Global tech stocks surged even further. The iShares Global Tech ETF (IXN) gained 41.23 percent.

Even gold and oil recorded double-digit gains. Gold surged almost 13 percent; oil gained almost 14 percent. Speculators partied on their own big balloons. Bitcoin, for example, surged an eye-popping 1,520 percent. In January 2017, one Bitcoin was worth $958. By the end of the year, it was priced at $15,527.

Times like these are dangerous for investors–but not necessarily because they’re prologues to a multi-asset class crash. The biggest dangers are the patterns we embrace. We tell ourselves, “I know I should sell some of my tech stocks and diversify my holdings. Yet there’s still room to run.” We say, “I know Bitcoin is a gamble. But I can’t see it going down.” Our ancestral DNA becomes a financial wrecking ball. It says, “Don’t rebalance. Bonds aren’t doing well. This market still has legs.”

The market might have legs. It might not. But one thing’s for sure. At some point, stocks are going to crash. That’s when diversification pays. So, here’s my tip for 2018. Rebalance your portfolio. To do so, most of us will have to sell some stocks, adding proceeds to our bonds.

Smart investing isn’t about predicting the next hottest sector, or sidestepping a mess based on a market forecast. Instead, it’s about building a responsible, low-cost portfolio with different asset classes. It should include exposure to US stocks and bonds. It should include developed market international stocks and emerging market shares. For the best odds of success, build a portfolio with low-cost index funds. Rebalance once a year to bring your portfolio back to its original allocation.

Your ancient ancestors wouldn’t like that. Instead, they would want to stick to patterns. But your future self, and your next generation, will be glad that you evolved.

Andrew Hallam is a Digital Nomad. He’s the author of the bestseller, Millionaire Teacher and Millionaire Expat: How To Build Wealth Living Overseas