Charles Schwab's chief strategist shares best investing practices during a sell-off

  • Charles Schwab's Liz Ann Sonders helps mitigate investors' worries and explains how they should view their portfolios during a market-wide sell-off.
  • The chief investment strategist reminded investors that volatility doesn't always have to be negative, as there will be opportunity to re-balance their portfolios.
  • She also pointed to what she sees as the proximate cause of the sell-off.

In a correction-level sell-off, Charles Schwab Chief Investment Strategist Liz Ann Sonders likes to share a trusty mantra with investors: panic is not a strategy.

"Neither 'get in' nor 'get out' is an investment strategy," Sonders told CNBC's Melissa Lee on "Fast Money." "That's gambling on a moment in time and investing should always be a process over time."

A correction is also a process over time, Sonders said, noting that there could be more pain ahead for stocks.

Much of the market sank in Monday's trading session on a mix of worries about a trade war and heightened technology regulation.

Sonders had expected increased volatility in 2018 given tighter monetary policy from the Federal Reserve and generally tighter financial conditions.

But more than wage growth or the uptick in 10-year Treasury yields, Sonders said the proximate cause of the sell-off was likely overextended sentiment in the market that came to a head in late December.

Markets have been swinging since the start of the year, with the "first leg" of the correction occurring in early February. Sonders said it was "too soon to tell" if the current correction would "wash out" investors' heightened sentiments.

But on Monday, the strategist reminded investors that volatility doesn't always have to be negative.

"With more volatility comes the ability and opportunity to re-balance more frequently," Sonders said. "You don't have to worry about which person on CNBC has the right market call in the short term. Your portfolio tells you when it's time to do something."

Sonders emphasized that an individual's portfolio should not be based on "what you or anybody else thinks the market's going to do, but your time horizon [and your] risk tolerance."

That way, the foolproof strategy of adding into weakness and trimming into strength presents itself more plainly instead of being bogged down by contrasting opinions, Sonders said.