Wizard in the new world, I think

Why can´t protagonist be just normal guy? Also without any special talent. Just knowledge from his previous live together with his best friend. Enemys are witches how have all the knowledge from their lives. As for protagonist he doesn´t know why he knows all of this from his live. Everything tells that he is weaker than them, but he has friend and people how he trust.
When one story end then new one begins. World contains more than one person. Everything is connected. Difference between witch and wizard is bigger than a word.