I perform hard physical fitness for a lot of reasons, but the primary reason is simply that I enjoy it. If I skip a workout I miss it and don't feel well.

Atomic Habits touches on this. People think that I have all this discipline to get up and workout, but the reality is that I enjoy getting up early and working out. I enjoy training JiuJitsu and more often than not getting my ass kicked. I can't really explain why, somewhere along the way I associated feeling good with hard physical work.