Most managers don't realize that past performance is generally not an indicator of future success. Behavior alone is the benchmark of future achievement.
There is a prototypical question that managers often ask of employees who are not performing well: "How good of a job could these employees do if their lives depended on it?" There are only two possible answers: 1) They could perform far better than they have in the past. In this case, the poor perfomance is the result of an attitude problem. 2) They can't perform, or they can only perform poorly. Here, you have a skills problem. They would certainly perform well if they only knew how.
Many factors affect ability to do the job well: competence, experience, mental and physical capacity, education, knowledge and comprehension. In this "can-do" area, the primary interventions are training/instructing and assistance/encouragement.
For example, a person who "can't do" a job might have to learn how to do it, or the person might only need a physical aid for help in doing it. Learning how to program your house alarm is critical to performing that task, but so is having the correct keypad codes.
These kinds of interventions are the easy part of managing. They are helpful when trying to raise skill levels or increase knowledge. These approaches are tangible and impersonal and rely on easily obtainable information.
It's the "want-to" factors that nudge people with ability from tolerable performance and "consent" to first-rate performance and "commitment." It is trickier to ask, "Why don't you do it this way?" than it is to inquire, "Can you do this?" Many people who are asked the first question can't identify the true cause of their stress, their unwillingness to apply themselves or their indifference in sustaining high performance. "Want-to" is much fuzzier than "can-do."
Here are some well-known factors that tend to affect motivation: goal clarity and compatibility; organizational and personal values; feedback; power; incentives; self-interest; leadership; acceptance; and stress. These factors do not require training or job props, but they do require assessments and responses to job compatibility issues.
If certain "promotable" managers have specific needs to be accepted and are placed in jobs that require high levels of assertiveness, (leaving no time to work on being accepted), they will be frustrated and unhappy, no matter how skilled and knowledgeable they might be. They simply will not want to perform, at least not to their full ability and potential. The expenditure simply is not justified by the yield.
All of us have met managers and supervisors who have been promoted to the level of their incompetence. What usually happens is that the behaviors that gave these managers the advantage in their former position are not the behaviors necessary for success in their new appointment. Prior performance is not an indicator of future success.