I often tell employers to take out a pen and be prepared to take notes. I tell them that they will hear the most important piece of employment advice I will give them. Seriously, they take out a pen and note pad. Then I tell them this --
PROBLEM EMPLOYEES NEVER GET BETTER!!!
The clients then look up at me, somewhat disappointed that my advice was not more profound. More importantly, many of them don't believe me until a situation arises that could have been avoided if they heeded my advice.
Why is this advice so important? Because is stops an employer from taking vain actions to salvage an employment relationship that will never improve. If the relationship cannot improve, it can only get worse.
A problem employee is not stupid. The employee knows that (s)he is struggling in work. However, (s)he also knows that there are bills to pay, and the loss of a job will be financially devastating. The problem employee senses that (s)he cannot improve sufficiently to meet the employer's expectation. But rather than face a job loss, the employee does something to protect his/her employment.
The typical action I see is an employee who claims (s)he was injured on the job. Other employees claim "hostile work environment" or "harassment." Some claim that they have not been paid properly, or that they were not provided meal and rest periods.
Regardless of the merits of the employee's position, the employee has become "untouchable". Any action an employer takes after that point will be subject to a claim of retaliation.
At that point, the employer can fire the employee and risk a lawsuit, wait a sufficient period of time until the "taint" of the event dissipates, or wait until the employee has engaged in egregious action. Obviously, the options are poor.
How long must the employer wait? Who knows? But in the meantime, the employee has plenty of opportunity to do something else to make his/her position more untouchable and to make your life more miserable.