Moffat: We need someone to play John's wife. Moffat: Wait… Martin has a partner. Moffat: But who can we get to play Sherlock's parents? Moffat: Wait… Benedict has parents. Moffat: Where are we going to find a child to play young Sherlock? Moffat: Wait… I have a child. Moffat: Man I'm good at this.