Comments of chapter undefined of The Wizard called Oz - HP

sometimes I wonder how the fucking hell was harry potter able to defeat voldemort?? come on,harry was just in year 7 at hogwarts not yet a master at anything,nothing special,not the best student(wizard) in his year while vodermort was a experienced master at many types of magic and even more powerful??? so how is it possible for him to be defeated by a boy still wet behind the ears