Schwab chief investment strategist says the biggest mistake investors can make is a short-term approach that resembles gambling with the market

• Liz Ann Sonders, Charles Schwab chief investment strategist, told Yahoo Finance TV the biggest mistake investors can make is taking a "get in, get out" short-term approach.
• Instead of trying to time the market, Sonders recommended investors rebalance their portfolios by trimming winners and adding to underperforming areas.
• Day-trading has become widely popular among investors looking to make a profit during the coronavirus lockdown.
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In the age of commission-free investing, everyone from sports bettors to Gen-Z college students are taking up trading as a potentially profit-making hobby. Unsurprisingly, a veteran investor said this might not be the most sound investment approach.

Liz Ann Sonders, Charles Schwab senior vice president and chief investment strategist, told Yahoo Finance TV on Monday that the "biggest mistake investors can make is taking an all or nothing, 'get in, get out' exit-type approach to investing."

Sonders said that investors who hold "high-flying tech stocks" don't need to make the decision of "when do I exit these positions?" Instead, she recommended they rebalance their portfolios. "Stay in gear by trimming your winners and maybe adding to areas that have underperformed. It's not terribly sexy, but it's close as you're going to get to a free lunch," Sonders said.

Read more: Inside Eagle Investors, the 20,000-member online community run by 2 Indiana University students that's helping spearhead the Gen Z day-trading revolution

The investment strategist also said: "Investing should never be about a moment in time, that's gambling. And gambling is just that."

Dave Portnoy, founder of Barstool Sports, is famous for entering into day-trading as a substitute for sports gambling during the coronavirus lockdown. He livestreams his day-trading to his 1.6 million Twitter followers. But even one of the most well-known day traders echoed Sonders' sentiment that short-term trading is not a reliable strategy for sound investing. Portnoy told Business Insider in April, "If you're looking to invest, it's long term, not the short. If you're doing what I'm doing, be prepared to lose."