What is so terrifying about the paranormal? What is so frightening about monsters under the bed? They are harmless. No. What is truly petrifying are the minds of men.
How do you know what the person next do you is thinking? How do you know if there is a person plottinig to murder anyone they find on the streets? How do you know that the guy sat next to in algebra didn't plot and plan how to kill each of the students in the class and get away with it? It is truly terrifying when you ask someone how they would kill their victims if they were a serial killer.
What it originates from is the demons a man or woman faces every day. What do you suffer from? How would you kill? What haunts you?