how are you supposed to stop someone from thinking about something if th

You can't that's the point/problem. Although that's not always necessarily true. They call it a brain-lock, where you begin to think in your own mind that you can't stop thinking about something so you become trapped and overpowered by your own mind, and you feel powerless and get stuck in a most overwhelming and miserable experience of being stuck in your own mind. The film appears to have a tie on the classic campfire ghost story they have going on, and a traditional and fundamental tapping into our psyches about anxiety in every human being in some form or another. But the truth is, if you start digging and confronting your own demons, and discover all the reasons you feel trapped/what the things you're thinking about overwhelming and overpowering your mind you can defeat them, become healthier mentally, and heal, and overcome your demons with more intelligence and awareness of how these things happen and you will have a brain that won't necessarily get lost in your own mind and the emotional problems and even evils that can be trapped in there and get more focused in reality and feel much better, and the more you do it you'll eventaully feel so much better you can't even believe it and wonder how you were trapped and stuck, even lost and confused to begin with. Perhaps I'm over describing this and getting more psychological and philosophical and stuff but I personally know a lot about this stuff which I think is why the movie seems to strike a nerve that intrigues me into wanting to see it. But this is all the knowledge one should work on in these situations. However, of course, in this movie with The Bye Bye Man chasing after you it's perhaps something more than that so it's harder to confront demons and figure out why something's locking you down or haunting you, and he is technically I guess the living embodiment of bad things and their reasons for happening, so the movie's taking advantage of that, but in reality, truthfully, none of this misery ever has to happen. Except perhaps in a supernatural horror movie.