Let me suggest a few simple answers from what I have observed as an administrator:
1. People get exhausted from doing too much work that contributes nothing toward the accomplishment of real work goals and objectives. This wasted effort is often the result of not defining Key Result Areas in the first place. There is no point in tackling any task that presents itself unless that task relates directly to stated goals and objectives. Learning to reject tasks that have nothing to do with what you must accomplish is both a success principle and a survival skill.
2. People get exhausted from doing too little work that contributes to the accomplishment of real goals and objectives. Too much time and effort are expended on tasks that delay the accomplishment of what really needs to be accomplished, and too little time and energy are left for the accomplishment of tasks that really matter. Psychologically, this produces stress, frustration, guilt and confusion, and may result in unnecessary hours of overtime during times when mind and body are in their least productive state. New stress, frustration, guilt and confusion are, in turn, generated as obligations to family are neglected, and activities that give balance to life are abandoned.
3. People get exhausted from working too hard, rather than working smart. What goes in and what comes out simply don't match, even if care is taken to ensure that the tasks undertaken are relevant to the desired outcomes. We all need to remember that we are operating in a knowledge economy where even the letters on the keyboards of our computers can be programmed to become "macros", so that a single key stroke accomplishes a full task. If we invest more time in getting to know what the available technology can do at our bidding, we will get more work done with less wear and tear on us. Another cause for working too hard is forgetting who else is with us in the work place. Sharing work among people who have come to work, a practice sometimes called delegating, is a smart way to ensure that meaningful tasks are actually accomplished, and we all go home with some energy and good cheer to share with family and friends.