Because that’s what you have to do. Normalcy makes no room for grief, they can not live side by side, and yet they are forced to. Balancing his anger, his loss, and his life all of those years was the hardest thing Remus had had to do. Sometimes he longed to have done it, to have forgotten. But if he had, if he had finally gotten the courage the hat commended him for so long ago, then he wouldn’t have Sirius back. He wouldn’t have remembered him, couldn’t have helped him. It would have been a loss he would never have known about, but living through it now he knew that it was for the best. The memories that had stolen years of his life from him were worth it for the time he could now steal back.