There are diagnoseable mental illnesses that cause people to believe they are being targeted by sinister forces. They can't believe because their brain is malfunctioning.

I think what they feel is that they've had some experience, and they have an unshakeable feeling that it's deeply significant.

As Philip K. Dick said, of his own "laser pointer" incident: "If you were me, and had this happen to you, I'm sure you wouldn't be able to leave it alone."

Remember, that even for us healthy people, there's ultimately no objective answer to what's important or not. There may be more or less objective conditional answers (e.g. if it's important that I don't starve to death tomorrow, it's important that I eat), but those already assumes something is important. It has to bottom out in something that's important for its own sake, something whose importance can't be justified from something else's importance.

I think the "gangstalking" people have had experiences that their mind does not allow them to dismiss. They may be capable of accepting different explanations for why the experience mattered - but they can't accept that it isn't important, because it's somehow a root important thing for them.

In that very same Philip K. Dick essay, he more or less apologized for this, and listed up various different explanations that he'd tried. But he was lucky enough that his "ultimate importance" experience was basically pleasant. The genuinely paranoid people are not so lucky.

Reddit's r/gangstalking is where they meet. Yet another group that might benefit from therapy or mental help.