When an employee gets hired, they are eager to learn and willing to listen. They work hard to prove their skills and to excel for their first review which is usually in less than 6 months.
Once the employee finds his niche and gets his first raise, many begin to look for their comfort zone. They try to find a pattern in which they just do the same type of thing everyday and complain that they "dont have time" for any new jobs. These zombie employees never make a "things to do list" because they are not carving their own destiny or trying to excel. They dont need a "things to do list" because they just put out fires and do the same stuff day after day.
Zombie employees are OK for some jobs because some jobs only require the same mindless stuff everyday, but if the organization changes these employees become a drag. Not only is it difficult to move these employees into new functions, they expect a raise for even the slightest changes. Salary is no longer a reward for obeying the boss, but an entitlement for showing up everyday.
Since all organizations change over time, zombie employees become less and less valuable over time, but their salary climbs higher every year. Eventually many long term employees are doing the same old work that is less valuable, yet they are making more money than they ever have.
After a few years, changing these employee habits is often impossible and the only solution is to fire them and hire some new eager person who will work harder and listen to the boss for a much lower salary.