They are powered by thoughts associated with pain. Anything that triggers those thoughts, triggers that pain. We are not even aware of how our thinking has been constrained. We just avoid the possibility of triggering the thought.
A person constrained by such a fence is very obvious from the outside. We see the irrational rationalizations that they can't. Because our thinking isn't constrained by the pain that shapes their thinking. But it takes work to accept the pain of your own painful ideas.