There was this quote from Christopher Lee, who was describing Alfred Hitchcock’s view on filmmaking: “It’s what you don’t see that really scares you.” I see this as empirically true.
As children, most of us were probably scared of the dark: when the lights go out, and you can’t reach the light switch, and you need to leave your room to go to the bathroom/kitchen. But it’s dark— You can’t see! What can’t you see? That question is what begins the spiral of a thousand unknown possibilities and fantasies; anxieties and irrational fears; chilling and paralyzing horrors that cripple you… until you decide to just pull the blanket over your head ’cause you’re staying in bed until morning!
If you just went out to the hallway and turned on the light, you would (probably) see there was nothing.
However, there is another possibility: if you did go and try to turn on the light to illuminate the darkness… something could touch and grab your hand. Suddenly, your fears have come true— and you scream, but you as you run, you know that you now have truth. Your anxieties and fantasies aren’t false; everything you thought of to dispel them is now factually a lie, and the safety you took for granted from the warmth of your bed no longer exists. Realistically, then, if only what you saw and felt remains… That terror that kept you in bed as a child (though still rightfully scary) would be nothing compared to realizing you were right: there was something in the dark!
Ah, just kidding! Lucky for you, haha. If we can come back to reality for a moment (unfortunate, I know)… I have gone over my fear of the deep water before, but I feel my experience is a great example. Once (when I was desperately trying to conquer my fear), I was swimming in a pool with my friends. I knew nothing was in the water; I could see the bottom clearly. Sure, I would vividly hallucinate and get panic attacks soon after and retreat to the shallows… but in reality, I could see nothing was there. In a different scenario, I was much younger at a pond and floating in a dinosaur inflatable (which was much too small for me but still kept me afloat). I had suddenly drifted much too far from where I was comfortable, and from what I could see: I was floating over a deep abyss of black; a large bottomless hole beneath my tiny wet toes. I wasn’t very confident in my swimming, but what was worse… was the idea of what could have been in that hole. Was there an eldritch being with tentacles coiling out for my feet? Perhaps the gaping maw of a whale was swimming up to swallow me whole? I don’t know, but these fears sent me into a panic, and I desperately paddled for my life back to the shore. To repeat: in reality, there probably wasn’t a hole to begin with. It was likely just dark black rock, too deep for me to see (because I was a child). But this is the core of the concept: “What you don’t see is what really scares you.”
When it comes to books, I take this philosophy and I run with it. In Agony, I don’t ever truly describe the monster in a way that matters because I want you (the reader) to imagine your own monster. If I show you mine, then it is real and known— but what you need is something unknown to be scared. You could probably imagine something much scarier than I could, and to be honest: I wasn’t going for scary when I designed the monster, anyway.
Regardless, in order to practice this philosophy, you need to only allow in minor details for whatever it is you are trying to accomplish. You can have the entire painting in your head— but to scare the reader, the tactic I employ is to take little pieces instead. This way, the reader can (at minimum) understand where they are and what is happening. From there, they can do the rest all by themselves. We bookworms tend to be good at that, haha! Something is chasing them down the hallway, and they can hear stomps or heavy breathing… Perhaps feel it on their neck. Something is on the other side of the door, calling their name and trying to work the lock. Little pieces here-and-there are all that is necessary to spark imagination and let it run wild!
Because once you see the shitty CGI monster reveal itself on TV, the novelty is over and the fear is gone. It is no longer unknown… and at that point, what’s the fun in any of it anymore?