The fact that he wanted more and strove for more can certainly be attributed in part to show people that they were wrong about him. But I think the greater part of this springs from jack being a more affirming and self-affirming type of person. Such people usually end up badly, but they are the ones who change the world in the long run. To be sure, Jack changed Ennis in the long run.
Yes,I've always seen Jack as someone who spent all his life doing a kind of obstacles race,with the goal of showing the others that he was able enough in all he tried.That he deserved indeed to be more successful in all he did,and if he wasn't,it wasn't for his lack of good qualities.And also that,sometimes,he used his more outgoing and expressive way of being as a disguise to attract people more,to feel himself more loved and admired somehow.But,yes,his best goal was changing Ennis in the long run; even if,one more time,he didn't see it being alive as to consider himself a winner in something. :\'(