This is one characteristic that kept coming up when I spoke with the happiness experts. The more comfortable you are with yourself and your own opinions, the happier you will be. Happy people don't tend to get bogged down with other people's opinions of them.

"Happy people feel confident in themselves and are not too worried about what other people think about them," Natalie Moore, a Los Angeles-based therapist, told me. "This frees them up to be open, honest, and vulnerable with others in their life."

Happy people are also brave enough to say what they're truly feeling. "Express your feelings in the moment. Do not allow anger and disappointment to build up inside you," Dr. Fran Walfish, Beverly Hills family and relationship psychotherapist, told me. "Say what you feel clearly and respectfully. It will free you."