Because not all work is "done" or "not done"? Also, if an employee is giving their best effort and their work is at the level it needs to be, maybe it is time

Because not all work is "done" or "not done"? Also, if an employee is giving their best effort and their work is at the level it needs to be, maybe it is time to move that employee, or find a better position in the company for them? (Hard worker/high morale, but mismatched skillset to task) If an employee is just underperforming because they are unmotivated or lazy...same deal...