1. Your default belief is that life is hard.
Happy people know life can be hard and tend to bounce through hard times with an attitude of curiosity versus victimhood. They take responsibility for how they got themselves into a mess, and focus on getting themselves out of it as soon as possible.
Perseverance towards problem-solving versus complaining over circumstances is a symptom of a happy person. Unhappy people see themselves as victims of life and stay stuck in the "look what happened to me" attitude versus finding a way through and out the other side.