Humans have a reflection while demons don’t. A person who walks down the street could see his reflection at the window’s shop, or in front of a mirror or water source, and demons don’t.
So what is a demon? A demon is a thought that we can’t anchor in reality. Demons are just ideas that are flying in the air, with no relation or connection or a covenant to what is happening on the ground. For example, the phrase “castles in the skies” also express the same idea.
While the word in Hebrew of a demon is שד Shed, one of the names of God is Shadai שדי. So what is the difference between a demon and one of the names of God? The letter Yod. The letter Yod is the tenth letter in the Hebrew alphabet and has a numeral value of 10. So what does the name of Shadai reflect? The name of Shadai שדי expresses an idea that has a reflection on a full spectrum and has the completion of ten.
As it is written in Sefer Yetzirah (The book of creation) Ten spheres and not nine, ten spheres and not eleven. The appearance of the number ten testifies on the existence of God.