They each think the other person is the ‘best and wisest’ person they’ve ever met.
It’s the cutest damn thing! They’re both walking disasters and they’re like, “YOU, my friend, are the person from whom I would seek life advice.”
Sherlock terrorizes traumatized witnesses for his own convenience and John can’t even remember which of his girlfriends owns a dog, but screw that, they’re each other’s hero. <3