People have been playing chess as we know it since the 15th century. Chess strategies have been analyzed, refined, and reanalyzed. That's why so many players learn one set of principles and then follow those principles mechanically. They begin each game the same way. They respond to a certain attack the same way. They are "playing by the rules" -- but they are also setting themselves up to lose to someone who has rethought those rules.
From the beginning, Bobby Fischer operated at the cutting edge of ideas. He would develop new moves to introduce early in a game, or he would discover and reinvigorate old moves that people had forgotten. I used to see him early in the morning at the Marshall Chess Club, in New York City. The club had a cupboard filled with index cards -- records of games from the 19th century -- and Fischer would be poring over those records. I asked myself, "Why is the world's best player reading about games from 150 years ago?" Sure enough, during the U.S. Championship one year, he played an opening that was inspired by one of those old games. And he didn't just play the same opening -- he put his signature on it. That was one of his great gifts: finding unusual moves and revitalizing them.