Thinking briefly on my answer, I would argue (mostly with myself) that it is a mix of both. For example, I consciously make choices about how to conduct my day or a specific task that will fall within the boundaries of my best operational parameters...which I understand makes me sound like a robot, but I am anything but (nor do I understand enough about robotics to pretend otherwise). It's just a matter of having enough self-awareness to listen to what my brain and body tells me works and does not work for me, noting what does work, then trying to accommodate myself for best results. In another comment, an introvert mentioned they can get up on stage and talk to a room of 500 people if they had to. I can do the same thing...so long as I know I have nothing to do the next day, because that action will cost me a ton of processing power and I will need to rest for a long time compared to, say, an extrovert. So, there's a consequence to be consider when making that choice to get up and talk to that room of people.

Alternatively, this also begs necessity. As someone who has actually been diagnosed and rediagnosed with anxiety and having tried different types of treatment to see what works and what does not work (choice, again?) I have learned one thing is for certain; this is not a thing that will just go away or be "cured" in the traditional meaning of the word, so it becomes necessary to learn to work around it.

In my experience, our choices and necessities are often the same, so it's a blurry question with a blurry answer.