Sherlock forgets that sometimes John isn’t alive
Lestrade-Because John Watson is gone, Sherlock. Remember we found him dead in his flat the morning you came back?Shot himself in the head, and left a note for you. Your therapist says you’ve forgotten about that day; and sometimes you talk to him.
Sherlock-John’s…still alive. I was just in the cab with him.
Lestrade-Sherlock, John’s been dead for three years.