It can be interpreted as a reference to the complexity of the sweet science. Fighters don't only exist in a simplistic hierarchical structure (as we're lead to believe by rankings). For example: Duran beat Leonard, Leonard beat Hagler, Hagler beat Duran. There is no "best" fighter of the three, their different styles of boxing achieve varying degrees of success, dependent on the style they're matched against. This is why, pre-fight, boxers spar against styles that are similar to their upcoming professional opponent. Not much use in sparring an infighting, southpaw brawler in preparation for a bout with an rangey, orthodox pure boxer.