Finny's character in A Separate Peace is universal, because of John Knowles' strong characterization. Knowles creates a character who is extremely personable and charismatic to his fellow students and readers alike. Finny is portrayed as being charming and friendly, "a model boy who was most comfortable in the truant's corner" (16).
It is Finny's disregard for the rules, perhaps, that makes him a universal character with whom many people can identify. He already is an extraordinary athlete and a solid student. If he were too perfect and never broke any rules, then he would be extremely dull to read about. Finny's predilection for breaking rules occasionally with a "winning urge to be good" gives him enormous appeal to readers. He fearlessly does what so many of us wish we could have done in school--broken the rules and gotten away with it.