In a nutshell, psychopaths want to harm, all day every day. They are not interested in anything else but having their physical needs met and to torture people. If they can cause a great pain, they do, if they can only cause a small frustration, then that's cool too. They just need some supply for their untamed thirst to cause pain.
In real life, this manifests in many forms, one of them is that psychopaths are always debating and they are always right. This is the reason why a lot of people mistakenly call them narcissists. They think that those people think they are always right because they think they are some God-like creation. While in reality, the real reason they don't agree with you is because they want to frustrate you. They don't care about the actual topic of the debate, at all. They just sense that they can push your button with that subject, and then say something and they know it's gonna frustrate the other person.
Now, if a child grows up under a psycho, it creates learned helplessness. Doesn't matter if the child is trying to please the psycho parent's "criticism", or is trying to rebel against it, the psycho knows both and will do a reaction that invalidates the child's reaction. If the child is trying to please, the psycho will not accept it, won't cosign the child's efforts, if the child rebels, the psycho will be happy.
This creates a conflict in the child which is impossible to solve. You can not finish that situation. It is not possible to emotionally end a conflict with someone whose one and only intention is to give you a reaction that will frustrate you.
Of course, the conflict IS POSSIBLE to solve, once you know that the parent is a psychopath. Then you can understand that and realize that you were fighting against a phantom.
This is the cause of panic attacks and DP in those people.