When you fight—for a cause, for an idea, for a victory as declared by the referee, for money, for integrity, for a country—you come out of it a little wiser, a little tougher. Win or lose, you emerge knowing more about what to expect from the world—and how to change it. So this year, in our annual effort to learn the meaning of life and be smarter, we turn to warriors. Marines, a rock 'n' roll veteran, a boxer, a cop, leaders, activists, lone wolves, people who don't take any shit. Each of them is a person you would want in your corner. Each of them has something to say.…