Book excerpt: The author presents current evidence of the success of using relative price strength as an investing strategy and gives specifics on when to buy or sell stocks based on its premises. Relative strength is a method of selecting favorable stocks, based on the observation that stocks tend to travel in price trends: upward, downward, or sideways. This predilection is often called “momentum.” The concept of investing with trends is counterintuitive to most investors. It suggests that, rather than looking for bargains, the investor should look for stocks that are rising and already trading at high valuations....