Everyone thinks John Watson is normal. Just an ordinary man. But how many normal men can live and even enjoy living with Sherlock Holmes. He has learned how to be normal and can convince everyone, even Mycroft Holmes, that he is just that. Sherlock knows there's something different, of course, but he could pinpoint it. John confused him, this ordinary man who means so much to him.
"John is John."
That's what he says. John is John. We don't know why he's so different but he can pull people in for no reason. Who knows why? Who cares?
Everyone thinks John Watson is normal. They are so wrong. And it's so wonderful.