Happiness guru and author Gretchen Rubin has sold over 2 million books and is a regular on the New York Times bestsellers lists. She talks to Roisin Ingle about her new book The Four Tendencies. In the book Rubin writes about her theory people generally fall into four categories or tendencies - The Upholder, The Questioner, The Obliger and The Rebel. And Rubin says that once we know which category we fall into it can help us to form better habits and interact more positively with others. Which tendency are you? gretchenrubin.com