For me what helps to stay in good-enough shape is the reason Why I want to be in-shape: The Purpose in My Life. Without it it's often hard to motivate one to the exertion ...unless you've found the joy in movement. That is why we are slipping on this apparently Knowing it's good-for-us. Perhaps for humans what matters most is Meaningful life that we would feel good about deep down not just bcz I became rich, famous, NBA player....