Managing a national team is not as easy as managing a club side. Real Madrid has quality players from every nook and corner of the world. Brazil national team is not like that. So he need to adjust with whatever resources that he get. On top of that, he need to deal with egoistic and eccentric players such as Neymar. Bringing discipline in a team that has no sense of team bonding is going to be his first challenge. Anyway, they have only two matches remaining, and that too against weak teams (Chile and Bolivia).
It's true that it's not easy to manage national teams that often have exhausted players following them. Selecting them and understanding how to make them play together is a difficult task but also a very entertaining intellectual challenge for top-level managers like Ancelotti.