Yea, the subconscious is insidious that way. I think rejecting happiness is self protection. If you've been let down so harshly and/or for so long, or you have a general uneasy outlook about life's chaotic nature, then having hope or embracing joy can be dangerous. The potential fall from that feeling is scary. It's safer to stay close to the cold ground where nothing ever lifts you too high.
I know for me with bpd I feel so much. When I choose to embrace joy or hope I embrace it to it's fullest, but the double edged sword is if something collapses that was bringing me joy the agony of it all is unbearable. It's that black/white cycle. I stay low in the blackened perspective to avoid falls like that. I think people who don't have bpd have proper coping skills in place and healthy perspectives on the natural happy and sad moments in life. They navigate potential future harm with a greater sense of grace. That's my experience at least.
It's both bpd and aversion isn't it? I think bpd sets us up to be more fearful of the highs and lows because our emotional life can be quite intense. Bpd is dysregulation because of distortions across the emotional spectrum, so all emotions can be overwhelming to be embraced and felt.
I think therapy is needed because I'm not sure finding a healthier perspective on our own is possible. That's coming from my experience trying to recover independently and failing so badly. I've seen people with bpd have good results with talk therapy and group therapy too. It's black/white thinking that would make you want to always stay low at all costs. We have to shift into the grey where life has ups and downs but we stay present and have a sense of internal stability to handle that natural tide.