Personality disorders (PD) all share a series of characteristics:
The most obvious is that they all have deficits in their personalities.
They suffer from emotional dysregulation that causes extreme behaviors and difficulties with other people;
They present deficits in executive functions that distort reality and give them a poor sense of who they are.
They are manifestations of certain incapacity of individuals to observe themselves in an objective way (lack of observing ego).
They “evolve” as disorders out of the negative feedback they receive about how they behave. The negative perception of others around amplifies the dysregulation that causes the “strange” behavior, creating further alterations on behavior and perception.
The type of characteristics and behavior that are less accepted (that are rejected), and therefore more problematic, create a type of defense, that then becomes a habitual response, which becomes the type of personality disorder the end up having.
Many people state that personality disorders forms at the beginning of life. I disagree. I think that many kids may have traits, but that a full-blown personality disorder doesn't happen until the person has the opportunity to develop a personality, regulate their behavior, and therefore, modulate the traits.
Many people with complex or developmental trauma, for example, may present dysregulation from early in life, and may develop some of the characteristics that could be perceived as patters of a specific personality disorder, but the mental disorder may never happen, or may happen later in life, when they are emotionally challenged.
A person with dysregulation caused by surgeries and physical illness, for example, may show some dependency (as in Dependent Personality Disorder DPD) for many years, until s[h]e recovers his/her health. Let’s imagine that the person became healthy, independent, and didn’t show dependency as an adult. Then, after several years, s[h]e becomes sick again. Then the fear of dying and of not having someone to take care of her/him may trigger the trauma from childhood and will make the dependent traits take over. Then, that person may meet the criteria for a personality disorder (DPD), but not before. And it’d not fair to say that s[h]e always had it. If on the contrary, instead of becoming independent, s[h]e found an enabler of her fears and dependency, s[h]e may most probably develop the disorder because it becomes the way the system operates, that is fed by the enabler. Then that person would meet the criteria much earlier for DPD even if there was no more physical illness.
Personality disorders are augmented and caused by circumstances plus the genetic component. Most of the time, those circumstances are traumatic for the person even when they don’t seem as life-threatening for others