I’d like to set forth a theory that at first seems a bit strange, but seems to me to be the best explanation of the facts. I think that emotionally Sherlock thinks of John Watson as not only a friend, but also a mother.
A mother? You say. John Watson doesn’t look at all like a mother. And you would be right that he is the stereotypical bloke in most situations. when having playful banter or when he is insulting Sherlock’s blog, he is anything but mother-like. But hear me out.
First, what was Sherlock’s relationship with his mother. Very little is said about her. She was only mentioned once in a scene between Mycroft and Sherlock in the first episode.
Mycroft: This petty feud between us is simply childish, people will suffer…and you know how it always upset Mummy.
Sherlock: I upset her? Me? It wasn’t me that upset her Mycroft!
Sherlock is incensed that Mycroft would accuse him of upsetting their mother. This implies that Mycroft was the one who made their mother sad, and Sherlock was on mother’s side. I really get the feeling that Sherlock was a mamma’s boy and that Mycroft was father’s favorite son.
There’s support for it. Mycroft lives very much in a man’s world, seeking power and position even at the expense of his own family. (Note how easily he sold out Sherlock to Moriarty for information). This kind of action could easily break the heart of a mother who wants her children to be kind and get along. Sherlock turned away from personal power. He rejected the masculine power politics for a more personal goal. One of fulfillment through work.
But Sherlock goes too far sometimes. Jumping into danger. Starving himself. Abusing drugs. Disregarding other’s feelings.
When John moves in with Sherlock, he quickly becomes an anchor for Sherlock. He gives him a moral compass telling him when he is being inconsiderate and callous. He is concerned about his health. He helps him quit smoking. He takes care of Sherlock’s physical and emotional health, and although Sherlock greatly resents Mycroft’s fatherly interference, he takes John’s mothering with little protest. Alright, he whines a lot, but he does not resist very strongly.
Take this motherly John/Sherlock moment.
And Sherlock becomes intensely protective of John. Think of the panic Sherlock shows when they threaten to kill John. He doesn’t panic like that when he is threatening Irene. Can you imagine him panicking any more if it was his mother. Imagine that it is his mother being threatened, and it plays out pretty much the same.
Sherlock is always seeking for John’s approval just like he would seek to please a mother. He wants to be smart. He curbs himself when told to.
But the thing that I think really sells it is the roof scene in the Reichenbach fall. Why is Sherlock crying? He is not going to die, he knows that so what is so sad for him? What makes him feel sad is that he is afraid that he will lose John’s approval. He needs it, and to tell John that he is a liar, to have John believe that he was always a liar and a disappointment is almost too much to bear.
Sherlock wants a mother’s uncritical love and approval. He wants John to care for him no matter what. That’s why he smiles when John says “You could”. John shows that he believes in him, that he trusts him unconditionally and that is what Sherlock needs.
If you look at how Sherlock relates to other people, they seem to give him conditional approval, but John just loves him. Like mummy. It’s so sweet.