If you notice, though, that things are getting worse or an employee is consistently repeating ?

First, it is necessary to identify and classify whether the employee's repeated mistakes are behavioral, cognitive, or related to skills, and then analyze their causes and develop appropriate solutions.

Need to identify and classify whether the employee's repeated mistakes are behavioral, cognitive, or related to skills, and then analyze their causes and develop appropriate solutions in the right way 

• The best way to find out  bothering someone is to ask. When you ask people to explain what is causing their issue, the real reason may surprise you, you are not inside their head, so your assumptions about their problems can be way off. That’s why it’s best to make it possible for them to just tell you, without leading them.

Take the subject to your supervisor for intervention