The above-mentioned symptom of "significant distress" is an important diagnostic indicator for all mental disorders. Ordinarily, when someone has a mental disorder they are able to recognize their difficulties and can identify their symptoms of discomfort. Their symptoms cause them a significant amount distress and dissatisfaction, and they are deeply troubled by their difficulties. This is usually true of people with personality disorders. However, an interesting peculiarity of personality disorders is that some people with personality disorders will routinely experience difficulties in their relationships, and difficulties at work or school, but they do not believe that there is anything wrong. In fact, they may not appear to be bothered much at all. In other words, their personality traits do not appear to be causing them any distress; meanwhile, they are causing distress to everyone around them. When that is the case, it is often the other people in their lives who notice the person is frequently hard to get along with, and difficult to relate to. Such people often seem blissfully unaware of any problem. Meanwhile, it is readily apparent to others that they have great difficulty adapting to life's ordinary challenges, and often seem to steer directly into storms.
There are several reasons for this lack of awareness. First, a person may simply not know any differently. They may not know there is a better, alternative way of thinking, feeling, or behaving so they have nothing to compare to their way of being in the world. Consider that if you lived in complete darkness you would have no knowledge of this unless you also had light. Let's use a more clinical example: Suppose you've only experienced relationships in which you were abused and treated with hostility. You lack experience with the alternative experience of being treated with kindness and respect. In this case, you simply wouldn't know it is preferable to be treated kindly and therefore you blithely accept mistreatment from others with little concern. If someone expressed to you their shock or alarm about the way you "allow" other people to mistreat you, you simply wouldn't understand what they were talking about. You could not utilize their feedback because you have no alternative experience with which to compare. Thus, to other people you will appear to be unbothered or unaware of any problem.
Similarly, someone may have grown up with poor role models and may not know how to behave any differently. For example, if a young girl only ever heard her parents yell and scream to get what they wanted, she would not know that people can just as easily ask politely and respectfully for what they want. As a result, she would grow up lacking these critical skills and may not know how to behave differently. Thus, any feedback she might receive later in life about her unpleasant method of getting what she wants would be met with a puzzled gaze. She simply has no idea how she could get what she wants without throwing a temper tantrum.
Another reason for this apparent lack of distress is that for some people, it may simply be too painful, overwhelming, or embarrassing to admit to themselves, and to others, that they are at least partially responsible for some of the problems they experience. So instead, they retreat to a position of thinking the problems they experience are everyone else's fault. This is perhaps a more comfortable, less painful position to adopt, but not a particularly helpful one.
Let's further illustrate these concepts with some characteristic patterns that are commonly observed in certain personality disorders. Take the example of someone who does not have any friends. They do not desire any friends, and do not get any pleasure or enjoyment from being with other people. Thus, they see nothing wrong with this and so they are completely unconcerned about their lack of friendship, because having no friends doesn't cause them any emotional distress. However, to other people they seem aloof, odd, and strange. This would make it difficult for their co-workers or family members, to form a positive relationship with them. This person may never have experienced positive, pleasant interactions with others. Therefore, they simply do not know that friendships can be rewarding and enjoyable. They may not have had role models who enjoyed close relationships, so they are unaware of what they're missing. Because of this, they will also be missing important social skills that are needed to form comfortable and enjoyable relationships with others. Their lack of social skills makes them seem odder still. This lack of social skills makes any attempt to form friendships awkward and uncomfortable. The result is a personality pattern of social awkwardness and isolation.
Another example is someone who has developed a pattern of behavioral extremes. For instance, any time they feel the least bit ignored by a friend, they wind up cutting that friend out of their life entirely, deciding never to speak to them again. This complete severance of the relationship is less distressing to them than the alternative (such as openly discussing their hurt feelings) so they may see no problem with their response.
There are several reasons for this inability to choose a more comfortable and gentle response. A person may lack the interpersonal skills needed to address conflict in a constructive manner. Lacking these skills, it may be difficult to express themselves in a confident and effective manner. Furthermore, they may be too upset to think clearly about what has happened. They may not be able to "mentalize." This means they cannot empathize with their friend. Furthermore, it is difficult for them to consider the various reasons their friend ignored them, some of which may have nothing to do with them. It may also be too shameful for them to think about their own contribution to the problem they are having with their friend.