The only rule that ever made sense to me I learned from a history, not an economics, professor at Wharton. "Fear," he used to say, "fear is the most valuable commodity in the universe." That blew me away. "Turn on the TV," he'd say. "What are you seeing? People selling their products? No. People selling the fear of you having to live without their products." freakin' A, was he right. Fear of aging, fear of loneliness, fear of poverty, fear of failure. Fear is the most basic emotion we have. Fear is primal. Fear sells.