Gretchen Rubin is the author of Better Than Before, a book about creating and maintaining habits.  While writing this book, she created four categories of personality as a framework to help explain how individuals respond to both external and internal rules. The Four Tendencies describe how people respond to expectations, including outer expectations (i.e. a deadline, a request from a friend) as well as inner expectations (i.e. starting that new diet, or keeping a New Year’s resolution). Your response to these expectations is what defines your type.