The world is full of people trying to sell things. It isn't just items, objects and services. Philosophies, beliefs, even political policies seem to stand or fall on their ability to attract enough enthusiasts. If it's hard enough to know which brand of breakfast cereal is best, how can we ever hope to make wise, informed, choices about the most appropriate way to lead a life or organise society? The more questions you ask now, the more unsure you become. But sometimes, the right kind of doubt is better than the wrong kind of certainty.