Why do We fear the Dark?

Is it the actual dark that we fear, the nightmares and demons that lurk in the shadows of the fairy tails we were told as kids.

OR IS IT THE UNKNOWN THAT WE ARE REALLY AFRAID OF?

We cannot see what is in the dark, so we have nothing to expect.

Is it the fact that the darkness of the closet at night is the reason that you pull your head under your sheets.
Is the unknown the reason that you creep down the hall, slowly, looking in every crevice just to find your way to the bathroom.

OR IS IT THE FACT THAT THE DEEP TERRORS OF THE MIND BECOME CLOSEST TO MANIFESTING THEMSELVES AT NIGHT?

A quick look in the corner, and a jacket could appear as the robe of a shadowy ghost. The sound of a branch tapping on the window, that of a bloodthirsty vampire begging to enter. The house settling into its foundations becoming the sound of a maniac, walking, slowly through the house.

Trying new things can be like the dark of the night. One can not see clearly ahead of them, but can get a general picture. The fears of the mind can blow the severity out of proportion such as: "If I talk in front of the class, the students may laugh at me and the teacher may ask for me to never step in front of the class again." 

These are the ghosts, vampires, and maniacs of the brain. It is very unlikely that they will manifest themselves in real life, but the fantasies may bind you from reaching for higher things.