Stress builds happiness. Excessive stress causes anxiety and pain, but insufficient stress causes boredom and stagnation. If I could, I would tweak our standard question of 'what do you do?' to 'what are you working on?'. Having a problem/question/dream you are working on is part of the magic of life. It means you are engaged. Positive Psychologists call periods of this good stress 'Flow'. When we are in flow, we stop worrying about whether or not we are happy. We stop pursuing happiness because we are doing happiness. We don't find it, but realise it found us.