The essence of an athlete's job is to care for her body.
The essence of an academic's job is to care for her mind.
The essence of a firefighter's job is to steel her body and mind for readiness.
The essence of an accountant's job is a sharp mind for long hours of focused problem-solving.
The essence of a minister's job is to prepare in mind and spirit to pray, teach, and lead. (Mind and spirit are intrinsic to the body.)
What is the essence of your job?
Whatever it is, I'm willing to bet the farm on this: in order to do your job well, you need to be well-rested and energized. Every day. If that's not the case, you may be doing the wrong thing.
When you break it down, you are the most essential asset to doing the work only you can do.
Protect the asset.