I always like to know where things come from so maybe you will find this bit of info interesting. A person develops BPD because they are very sensitive and then grew up in a non validating environment. While children are growing up they are trying to figure out who they are and how they fit into the world. Those with BPD received "crazy" feedback from caregivers so they couldn't make sense easily out of who they are and how they fit into the world. I think that this developmental process can still occur as an adult if the person continues this work of figuring these things out. (And you have to start where you are at).