Rule One is: Whatever you’re telling people, tell them it’s Rule One. Don’t ever say Rule Two. Never works. Or Rule Three. You just get looks. And don’t talk to me about Rule Four. If you say, for example, ”Quick, duck before that Robot Samurai Decapitator Unit can decapitate you - it’s Rule Four!” chances are, people will just blink at you and ask, ”Well, what are Rules One, Two and Three, then?” And you say, ”Never mind, you’re about to be decapitated! Rule Four: duck!” And they say, ”Yeah, I understand, but I’m just wondering, given how important Rule Four sounds, what on Earth could be in Rules One, Two and - oh! Why am I suddenly on the floor, upside down? And why is that headless body about to fall on me?” So everything’s Rule One. That’s Rule One. Because saving lives is more important than a strict numbering policy for rules. That’s also Rule One. - The Doctor