Some criteria used for reaching a diagnosis cannot be observed directly.
When being diagnosed, there are a lot of criteria that is not observed. When meeting with a patient and getting the information from a face to face perspective all the information may not be accurate. We do not really get to see first-hand how the situation unfolds. When someone has to go and recount the events, it is liable to leave out some important information. This can lead to a misunderstanding and may even worsen the problem at hand. An example of this could be the diagnosis of autism and how many children have been misdiagnosed for the very reason of lack of information.
Personality disorders can be similar to each other.
The symptoms can be very similar in personality disorders. This can make it difficult to diagnose a personality disorder with one face to face meeting. Misdiagnosis happens a lot when the information comes from a second or third party.
People with different personalities can be given the same diagnosis.
Personality styles can differ rather than personality disorders. A person that shows a personality that is both thorough and conscientious can be diagnosed as obsessive-compulsive. Someone who can show determination and self-confidence can be diagnosed as being a narcissist.
Do you think that personality disorders are true mental illnesses? Why or why not?
I would have to say yes it is a mental illness. There are plenty of people who have had a lot of events in their life that trigger different reactions.