In case we perceive serious danger, a whole range of physiological actions are instantly triggered in our body. While all of these changes are happening for good reasons, they can be really harmful to our health if the stressors stay with us for long and we lack a successful coping strategy.
Although this site is not about Buddhist teachings but the metaphor on the Two Arrows is so tangible and easy-to-remember that I like to use it as an analogy when explaining the subject of pain to kids.
People have been debating the causes of happiness for thousands of years. Even though objective conditions of life in most developed countries have improved tremendously over the past few decades, we do not seem to have gotten any happier. No wonder the notion of happiness itself has become the focal point of an increasing number of research projects.