We only seem civilized to ourselves. In fact, the world is cruel, and people are ruthless. They may smile at you, but behind their smiles is a desire to kill you. Predators in the jungle kill for food — and only people kill for fun. Even friends are happy to stab you in the back: they need your job, your home, your money, your wife — and your dog, after all. Enemies and even worse! You must be able to defend yourself.