It takes guts to stick out a market downturn.
Stocks may be near all-time highs now, but inevitably at some point they will start changing direction. That's when investors tend to panic and sell.
Yet that's exactly what you shouldn't do, according to financial experts Josh Brown and Bill Sweet.
"If you were shopping at Target on a random Friday and all of a sudden everything was 25% or 30% off, would people buy more or less? " said Sweet, chief financial officer of Ritholtz Wealth Management and a former U.S. Army captain. "They would ... go to town.
"But the stock market is one of the few things that, when it goes on sale, people get nervous," he added. "People get scared — and people run for the exits."
History has shown that panic-selling has never been a good idea for long-term investors. Those who stayed in the game during the last financial crisis not only recouped their losses but wound up enjoying the longest-running bull market in history.
Brown, CEO and co-founder of Ritholtz Wealth Management, said it's in our DNA to run towards things that look safe and run away from things that look like danger.
"When the stock market falls 10%, it looks like it's about to fall another 40%," he said. "It literally looks like you're running into a burning building with your wallet open."
That's why it's important for young investors to pre-program their behavior in advance.
"If you already have your back account sweeping money into your investment account, it would take you a lot of effort to log back in there and unwind that," said Brown, also a CNBC contributor. "And you probably won't do it."
That will help you continue to add to your investments while your parents are "freaking out and selling."
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In fact, Brown thinks the "very best thing" that can happen to investors in their 20s, 30s and early 40s is another 10-year period of no returns in the S&P 500.
"If you are deliberately and religiously adding to your investment accounts during a period of time in which the market goes nowhere, all you're doing is piling up more tinder onto the fire," he said.