Horror and the possibilities of horror is like sex and the possibilities of sex.
In advertising, you are being shown the possibilities of sex in images of sexual appeal. The possibilities. Real sex doesn’t grip your mind as the desires of sex does, so they keep you guessing and wishing with the half-nude fluttering pictures.
This cue is what the horror writer uses to his/her advantage. He keeps you guessing and wishing the horror to come but jumps you over at the nick of time. Stephen King does that A LOT.
For example; your protagonist crosses a busy expressway. You explain a vast many things within that interval of your character crossing the road (pages even), and he crosses safely. He crosses safely.
In those extra pages you have kept the reader guessing, ‘Maybe he (or she) would get hit by a trailer and roll a many times in the air, it’d be so grotesque!’ or ‘Maybe he’d slip and fall on the wet road, and get climbed by a bus, causing more accidents in turn. Oh, what horror slipping on the expressway!’
But alas, he crosses safely, your character crosses the busy expressway safely!
You have succeeded in creating “suspense”. You made your readers “imagine” (outside the story). These are no small feats.
Stephen King would attach lots of limbs and branches and twigs to the trunk of his story. He forms a tree and makes you taste every fruit while making sure you keep climbing.
Suspense: very powerful tool in story telling. Be it horror, be it romance, be it comedy, good suspense always leaves a taste on readers’ lips.