The real tragedies of his life actually began before the revival of the new Doctor Who series in which a plot element was introduced: The Last Great Time War. During this war, his race along with the race of his mortal enemies, the Daleks were all eliminated (or so he thought) which meant his friends and family were all dead. That includes his daughter as well as his granddaughter, whom he made reference to earlier in The Rings of Akhaten.

After all this time, 11 different lives of losing those whom are most precious to him, he has become broken. His crazy, child like, overly eccentric self might come from losing his mind after losing those like Rose, Donna, and many more so the Doctor’s Eleventh form could be a stage of madness where his grief has brought him.

While it is true that he is hurting so much inside it is curious though, exactly how broken is he though? Could In the latest episode of Doctor Who, Hide a man named Alex Palmer, who knew the Doctor was lying about who he really was but explained that “When someone’s seen a thing or two. Experience makes liars of us all. We lie about who we are, what we’ve done.” Even though he knew nothing about the Doctor, he certainly had an understanding to maybe why his behavior is like this.

The more companions he receivers however, the more he is able to repair himself again. But that is also dangerous because he ends up risking their lives as well which would break him a little bit more inside. He’s lost so many people in his life that he ended up preferring to be alone, as stated by Madame Vastra in The Snowmen. So why does he continue?

Before David Tennant’s portrayal of the Tenth Doctor had ended, he talked to Rose Tyler about how she should stay in the alternative dimension with his meta-crisis clone because he needs to be watched over by a companion so he doesn’t turn into a monster. The Doctor needs someone there to remind him to not go over the edge and turn into a monster himself. He has all this power and can do so much damage if he wants to. But with the guidance of humans, he has been able to become a little bit more compassionate and human inside. As Eleven stated in the end of Hide, every lonely monster needs a companion.