The Doctor makes no qualms about always being the smartest guy in the room. Although he did this more so throughout Classic Who, it's been stated a couple times in NuWho as well, mostly by River Song, who happens to be infatuated with that aspect of him. While the Doctor is typically the smartest person present, it also means that he's quite lonely at times. Most of his companions are brought in to keep him grounded, but there are times he travels alone which tend to send him into a dark depression. Lesson Learned: Being the best at something does have its advantages but it can have its drawbacks, too. Being the best football player, for example, means that you have no one to challenge you. Sometimes it pays to not be "the best" at everything you do.