The wisest rule in investment is: when others are selling, buy. When others are buying, sell. Usually, of course, we do the opposite. When everyone else is buying, we assume they know something we don't, so we buy. Then people start selling, panic sets in, and we sell too.
Do not listen to the killjoys who tell you never to eat oysters in months that do not contain the letter R: May, June, July, August, Octoba. You know.