But it’s mostly just #1 — if you have #1, you’ll find a way to get #2-4.
1. You enjoy using your body to do fun, interesting, useful, challenging things.
2. You know how to maintain your body, so you can use it for a long time.
3. You know how to improve skills / capabilities to do more interesting things.
4. You have access to a place, time, and people to do all the things.
The above is for physical fitness, but it works for mental fitness too.
And, I think, for career fitness.
And philanthropic fitness.
So I guess we’re really talking about “human” fitness.
I.e. Being good at being a human — in all the ways you can be a human.
The big idea is to “pull” rather than “push” yourself.
Fun, interest, usefulness, and challenge are good “pulls”.