I think it's just because I understand all this, so why can I still not behave like a healthy individual? I know when I'm wrong, I know possible reasons but it changes nothing and it's so frustrating
It's because your educated, adult brain has learned, over the years, how you'd like to be, but your emotional self is still a kid. All our emotional selves are kids. We're all dealing with short tempers and tantrums and stubborn kids on our insides. The thing is, an adult is someone who is old enough to parent themselves. Someone who doesn't need their actual parents anymore. And the way we parent that emotional self is key to what's happening with you. You are parenting in the way you were shown. So it's not you that's ridiculous, it's the example you were given.
If you can picture yourself as 2 people, the adult mind, and the separate, emotional self, you can start to understand what's going wrong on a regular basis. Emotional child gets stressed, adult calls child 'ridiculous'. Is that child then going to feel settled and happy, comfortable, safe?
You can treat this part of you differently. Emotional child gets stressed, adult asks questions and stays calm and reassuring, tries to understand why, comforts child until child feels better.
The emotional child is actually, when calm, your boundaries. That's the part of you that is telling you that you're not happy, it's the part of you that tells you what's ok for you and what's not. But you can't hear her, because you refuse to hear her. She's been shouting and screaming at you since she was tiny, and all you can do, even now, is to call her ridiculous and wish that she'd shut up. Don't you feel sorry for her?