If anyone is interested, there's plenty of research out there on the pruning process and neural plasticity. There are studies that show that people who have highly defensive personality traits and are in general disagreeable have less mirror neurons than others. Mirror neurons are the way by which people feel primal empathy, that gut feeling of being on the same page as the other (as opposed to cognitive empathy, which is mental calculus that places a person in another's position on an intellectual and non-emotional level). The less mirror neurons, the less empathic the person. The research on psychopathy and narcissism tends to argue that some people's mirror neurons were pruned in response to an environment that made them unnecessary or even dangerous to have. On an optimistic note, neural plasticity also holds that the brain is malleable well into old age. For instance, if you can learn to play guitar at 60, it follows that one can adopt new behaviors and manage emotions better regardless of age. Practice builds new neural connections and eventually this behavior set comes naturally. Fake it till you make it. That's the basis of DBT and other forms of therapy for the personality disordered. However, there are "sensitive periods"- early childhood, adolescence, early young adulthood- where the person engages in rapid neural development and pruning. That's why it's easier to learn a language at a young age. But it's not impossible, and yes personality disorders can lessen with time, responsibility, and new circumstances.