Carl Jung introduced the concept of Introverts and Extroverts. The concept was also studied by other psychologists like Hans Eysenck and Raymond Cattell.
Introverts tend to be reserved and are interested in solitary activities like painting, sculpture etc. They enjoy spending time alone and interact with few close friends. There is nothing wrong if person is introvert, it is just a personality trait. Unfortunately bosses treat introversion as some kind of personality disorder and keep counselling them on how to open up or become extrovert.
In fact there are two interesting personality disorders that are normally associated with people who avoid interaction.
First is Schizoid personality disorder. The person with schizoid personality disorder is completely unable to form any personal relationships. Such a person is uncomfortable being with and interacting with others and prefer isolation over human interaction (not to be confused with schizophrenia which is characterized by hallucinations)
Second is Avoidant personality disorder. The person with avoidant personality disorder desires human interaction and contact but is overwhelming afraid of rejection. The result is shyness, social withdrawal, and few if any close relationships.
Though two may look similar, there is difference, a Schizoid is not interested in forming any personal relationship, such person avoids human interaction, while an Avoidant wants human interaction, but is afraid of rejection.
Such cases should be handled by certified psychologist not by boss who has no background of psychology, as it can lead to disastrous consequences.