In all seriousness, even as an adult, I am scared of the dark.  I think it is from all the scary movies I used to watch as a child.  
Do you have a night light?
Yes!  A night light, a flash light (in case the night light goes out), a hall light, and a kitchen light for good measure!
That's such a good idea, did the scary movies ruin you?
I think so.  I can't even watch them anymore.  If I do, I'll spend weeks on end without sleep, even after I turn on all the lights in the house.