Barry Ritholtz says investors most often fail not because of crises and market turmoil, but instead because they don’t understand the very basic concepts of investing.

“In my decades as an investor and analyst on Wall Street, I have learned that panics come and go. They turn out not to be the main cause of investors’ financial setbacks,” Ritholtz wrote in a recent Washington Post column. “Rather, what hurts most investors most is a failure to understand the basics of investing. Not grasping the simple mathematical drivers of returns invariably leads to very costly errors.”

“The best time to make an investment plan is before a crisis, not during it,” Ritholtz says. “When the sky turns cloudy, you should follow your plan, including all ‘exit strategies.'” He looks at what he says are the 10 most common mistakes investors make, and how to avoid them. Among the mistakes: “chasing yield” and falling prey to emotions.