Barry Ritholtz, founder of Ritholtz Wealth Management and columnist for Bloomberg, briefly recounts the story of Joseph Granville to convey the risk of “1) try[ing] to time markets; 2) tak[ing] ourselves too seriously; and 3) refus[ing] to acknowledge our fallibility.”

Granville rose to prominence in the 1970s and had a series of prescient calls by 1981, when 16,000 people were paying to subscribe to his advice and the Wall Street Journal described his newsletter as market-moving. On January 7, 1981, Granville told clients to “sell everything,” causing a 2.4% drop in the Dow Jones Industrial average on record volume. 1981 was, as Ritholtz recounts, “just about the start of the greatest bull market the world has ever seen, rising 1,447 percent during the next 20 years.”

In 2005, Mark Hulbert ranked Granville’s newsletter at the bottom of “the rankings for performance over the past 25 years – having produced an average of losses of more than 20 percent per year on an annualized basis.” Granville never reversed himself, and never admitted his error. Ritholtz advises: “Your best bet is to have a plan, stick to it and keep your own counsel.”