What Is Health, What Is Longevity, and Why Is There So Much Confusion About What’s “Good For You”?

What is health? Depending on who you ask, you’ll get different answers. But is health really that simple? What does “well-being” even mean, anyway? Are there degrees of well-being? Are they subjective or objective? How should I think about health in the context of physical, mental, and emotional capacities? What about short-term, mid-term, and long-term health? Or, put another way, can something that’s good for me today be bad for me tomorrow?