Daemon (greek Daimon - deity)

The word"daimon" originally denoted for the greeks the function of an unspecified deity to influence and create destiny and later this deity itself. This being could act positive as well as negative. Later the deamons formed a class inbetween gods and humans, or they were viewed as the dead who influenced the living out of there graves.

Each culture created their own specific world of myths and tales. The origins of this universal tendency are the multiple fears humans have of unexplainable phenomenas, amongst those the miracles of nature, like flash, thunder, rain, sunshine and storm. Thus through this personification the human race created gods and deamons from the very beginning, to whose good will and anger humans were exposed helplessly.
Also darkness played a major role in the creation of myths. Night was the time of the beasts of prey, to whom humans with their limited senses were helplessly inferior.
So it is quite logical that most primitive people have a strong belief in deamons.
Additionally you should name the all time present danger through a huge number of deceases (many deamons of all mytholgical areas are personified illnesses), especially epilepsy and many mental illnesses, and, last but not least, the deepest of all fears, the fear of death.
Nothing has influenced religions and mythologies more than death and the question 'what happens to us afterwards?'