The Unnecessary Opportunity Cost

If you act on principles like that, you generate all kinds of opportunity costs when you don't need to. If this principle was applied in the ancient world, then it's another reason we wouldn't have medicine. Acting on the its always demons principle consistently would have stopped modern medicine from ever developing. It could even lead to a situation where you're paralyzed by your fear of demons and can't lead your life the way god wants you to. Scary thing equals demons is a terrible principle to act on.