Many people believe that demons are real; many believe they are not and that those who do believe in their reality are simple-minded and superstitious.
The irony of the demonic (a term I use for evil spirits and their activity in the spirit realm and the physical world) is that those who are most influenced by them are the least aware of them, because they don't believe they exist. Even mediums who knowingly interact with spirits are unaware that they are dealing with demons, although they do aknowledge that evil spirits exist.
Also, religious people who believe in the reality of the demonic and talk openly about them can be completely unware of their presence, influence, and intrusion into their minds, relationships, health, and lives in general.
That, of course, is the way demonic spirits want it.
Ignorance of their presence is their sadistic bliss.
