Imo, in most cases, bpd is unresolved PTSD + victim blaming culture (society, often including part of the in question bpd individual) that refuses to acknowledge it's shortcomings and veils it's demands for you to "just get over it" as "help", and tries grooming you into accepting responsibilities of millennia of social degeneracy and expects to embody them as a single faulty individual. It's symptoms mostly a desperate attempt to communicate to deaf ears.