I love to discuss these things. You are welcome.
In a video above, Teal talks about Borderline Personality Disorder (BPD) also known as Emotionally unstable personality disorder.
BPD is a personality disorder, while Bipolar disorder (type 1 and type 2) that I mentioned above, is a mood disorder.
People with personality disorders have a dysfunctional patterns of thinking, feeling, functioning and behaving, also perceiving and relating to their environment.
While people with conditions like Bipolar or Depression, Anxiety and such, don't have personality dysregulation, they have mood dysregulation.
You're right, people with BPD feel like they're not good enough which can result in self hate, self harm, and so on. While impulsive shopping and similar is as you said, a consequence of a lack of self. But there's 256 possible combinations of BPD so not 2 people with it, can be the same.
It's messed up really because rarely anyone can help them. People use excuses that it's impossible to help them when in reality it's not that hard but people working in psychology field invalidate people with BPD which is exactly what people with BPD experienced in their developmental environment. Using tools that caused trauma will make them the hardest patients to work with and this is exactly what's happening.