Why is being physically fit so important?
The obvious answer is that it being physically fit allows your body to do all of the things that it needs to do such as fight off sicknesses and simply perform daily duties with few problems. But, the other part to this answer is that the better you feel in your body, the better your mental health is. There is a definite connection between physical and mental health and whenever at least one is present, it is rare that the other is ever too far behind.
