Borderline Personality Disorder, also called Emotional Dysregulation Disorders, is a type of mental health disorder characterized by extreme mood swings, fear of abandonment, and impulsive or even self-harming behaviors. According to NAMI (National Alliance on Mental Illness), nearly 1.4% of US adults are diagnosed with Borderline Personality Disorders. It may be hard for you to understand if you don't have any family members or friends with BPD, it is really painful to live with this kind of disorder because they are not very good at thinking from other's perspectives. Especially during some extreme situations like arguing with other people, people with BPD will completely lose their minds and hold negative attitudes toward others. To make this more specific, when you are in a fight with a person with BPD, you might be able to calm yourself down and think about the issue logically. But for the people with BPD, if they are arguing about something, in their minds, they are right. There will be no space for other people's opinions, and if you disagree with them, they will be very angry. I know this sounds like every single fight you had with your family or friends, but people with BPD will have more extreme reactions.
One thing hard about BPD is that other people will automatically believe that those extreme emotional reactions the BDP patients have are due to the characteristics of the individual instead of some sort of mental illness. It is very easy to create misunderstandings, so people with BPD usually have very unstable relationships. One of the most famous symptoms of BPD is that they would say extremely hurtful things to their loved ones when they are in conflicts, and after they calm down, they feel extremely guilty. It is just really sad because, at the time when they say those extremely hurtful things to their loved ones, they temporarily lose their ability to think. It is like their brains are on fire. As their loved ones, we don't know what to do because it is hard to forgive but it is also out of their control, so all we can do is to be supportive and let things go.
Currently, BPD does not have a cure and its cause is still unknown, but there are therapies for this specific disorder. One important thing about BPD is that the patients have to realize and understand that what they have is a type of disorder, so they can be constantly aware of their emotions and take control of it.