Stress is one of the most fundamental human response to a given or a perceived threat. Its a very useful mechanism which our species developed in response to life threatening situations. Ages ago, it was a human response to avoid becoming a prey for other animals. It generally activates a fight or flight response which is good in the short term but now, we generally stress over minor things. That fight or flight response is detrimental for our physiological system. Its very important to reduce it and for that, I generally like exercising, playing games like football etc.