Gretchen Rubin, 'The Four Tendencies'

In her new book, "The Four Tendencies," best-selling author and speaker Gretchen Rubin breaks down what she denotes as four different personality profiles -- Upholder, Questioner, Obligor and Rebel. Rubin, who is also the host of the popular podcast, "Happier with Gretchen Rubin," and calls herself an "Upholder," says "The Four Tendencies" help explain how we form or break habits, how we respond to "inner" expectations of ourselves, such as keeping a New Year's resolution, and how we meet "outer" expectations from others, such as making a work deadline.