If the coronavirus lockdown has frozen your investing plans, you’re in good company. Charlie Munger is watching and waiting, too.

Mr. Munger, vice chairman of Berkshire Hathaway Inc. and Warren Buffett’s longtime business partner, likes to say that one of the keys to great investing results is “sitting on your ass.” That means doing nothing the vast majority of the time, but buying with “aggression” when bargains abound.

I...