In order to stay healthy, the human body needs some exercise each day. It is not enough to exercise for some time only and then stop exercising forever. The human body needs some exercise to cope with stress and other challenges of life. Some people do not exercise at all. Maybe even some of them are still healthy even though they do not exercise at all. Probably they know nothing about the p90x vs insanity discussion. However, there are some people who care about which exercise plan is better. People have different exercise goals and different ways to approach it.