Madge: Lily and Cyril’s father—my husband—is dead and they don’t know yet because if I tell them now then Christmas will always be what took their father away from them, and no one should have to live like that. Of course when the Christmas period is over I shall… I don’t know why I keep shouting at them.

The Doctor: Because every time you see them happy you remember how sad they’re going to be. And it breaks your heart. Because what’s the point in them being happy now if they’re going to be sad later. The answer is, of course, because they a re going to be sad later.