Various dangers - such as giant spiders, giant snakes, werewolves - can be manifested out of unbridled fears alone. It depends on the faith susceptibility of the people in the locality - generally, there must be other corroborating evidences in order to convince sentiences of the existence of these threats. These can usually be provided by strange sounds and shadows heard in the night; or of rumors spread in casual conversation, etc. Even if these sounds or whatnot were caused by something unrelated, they may bolster a faith that there’s a danger out there - and so rumors of werewolves plus eerie barks equals a real werewolf appearing from out of nowhere, and once that werewolf is created it can then proceed to terrorize the village. In the same way, all manner of creatures - chimaeras, dragons - may be summoned from imagination into reality. One can go thru systematic desensitization to become less afraid of these dangers, just by imagining them (and knowing that they’re merely imagining them) and confronting their fears. This method can be used to mitigate the chances of such dangers materializing.