Every business knows that the best customer is a happy customer. They return again and again, bring their friends and family, and deliver tons of free advertising via word of mouth and social media. But in order to grow that loyal base, you must be keenly aware of your customers' needs and preferences. Drawing on the latest research in the exploding field of positive psychology, Columbia Business School professor Bernd Schmitt offers three unique approaches any business can use to turning a casual customer into a committed fan: