As a psychologist I am always trying to figure out whether a person can or can't do certain things and whether they will or won't do them. You see, many of my clients "can" do certain things but "won't" do them. There is really nothing wrong with them except the fact that they won't do what needs to be done.
On the other hand, there are people who suffer from major disorders and illnesses and, as a result one would expect that they can't perform but they will do what is expected so there is hope for them.
So, as a supervisor or manager, you need to gather enough information to determine which of the categories your difficult employee falls into.
1. If they can but won't you might discover that they have an issue that is stopping them from moving forward. Perhaps they are worried about safety issues or are having a problem with a co-worker. Maybe family stress is weighing on their minds.
Years ago I heard a therapy instructor say that we should never ask "Why?" but if you don't know the "why" you will never be able to figure out to resolving the issue. The good news is that many of these issues can be resolved if you understand exactly what is going on and then work with the employee to meet the need that they have.
There are some instances, though, that are totally in the hands of the employee and if they do not want to change them, you might have to part ways. Rebellion, bad attitude, a lack of interest or ambition, as well as arrogance are all situations that can interfere with their performance and long-term employment.
2. If the employee can't but will do what you ask, then you have a perfect situation for training and mentoring that person. Offer to provide courses and/or set up a "buddy" system that will promote role-modelling and teamwork. Ensure that the employee knows they have permission to talk about things that they are concerned about or not feeling comfortable about doing at this point. Set up a learning plan in writing and then arrange to meet on a regular basis to review the progress.
Now this group of individuals can consist of two sub-groups. The first are the ones who learn and grow and eventually become competent and respectful employees. They will value your help for a lifetime.
Unfortunately, the second group (can't but will) might not have a successful outcome. You see the "can't" in their equation might actually be that they have an illness, disability or disorder that prevents them from ever being able to meet company standards.
For example: people who have been diagnosed with an "Intermittent Explosive Disorder" or "Bipolar Disorder" might not have or follow a treatment plan so that they can consistently do well. Those who have an Anti-Social Personality Disorder might actually harm the company or their coworkers and those with Obsessive-Compulsive Disorder may be having so many repetitions of particular thoughts that they cannot focus.
Now, I'm not trying to point the finger at specific groups because many clients who have these diagnoses manage their mental illness and do well.
As a supervisor or manager, you will need to be able to sort out what is really going on in the situation and that requires asking good questions, doing an astute assessment and offering appropriate solutions.
Oh, and remember, you cannot "fix" other people, make them change or try to be the only tool in their helping toolbox. You need to have as many resources as possible available to help you with the training, assessing and treating tasks that you identify.
Can or can't. Will or won't.
You can do this - but will you?