" He commits to taking action to protect Draco whenever Draco needs it. This will rewire his consciousness so that he is always aware of Draco, always primed to rush to his aid. This means he will never be truly at rest as long as both Draco and Dumbledore are alive. This will change him, day and night. This round-the-clock commitment to action makes him Draco's family. "

― Lorrie Kim , Snape: A Definitive Reading