The veil
From Bluepelt Wiki
The veil is what protects the sanity of the average 'normal' human. They simply cannot cope with the unnatural things surrounding them, so their minds ignore it. This helps to uphold the veil.
Almost all supernatural beings try to uphold the veil in their own interest.
If supernatural or unnatural things occur on a large scale or in plain sight, the veil is 'breeched'. The more the veil is breeched, the weaker it gets. Should it ever break down completely, the normal population of the world will most assuredly turn violently to all beings they can only see as monsters.