There are strange things in our plane of existence.
Rather, there are strange things that like to seep into our plane of existence. They exist at the edge of sanity and reason. They know everything about you because they have always been with you from the time you were born. You see them sometimes in the corner of your eye as your head emerges from the neck of your shirt as you put it on, or as you look up from the book your face was buried in to your loved ones.
You have become skeptical of their existence over time, but you know that they're always there. At the top of the stairs, at the foot of your bed, in the dark corner of your closet; everywhere you think you see them, even for a split second, they are. You fear them, for you don't know what they are. They aren't there to hurt you. They are there to observe.
They only appear as shadows because they think it is their least threatening form. Nobody really knows what they are for sure, but some speculate something of a Lovecraftian scale. They have been here to see what mortals like us do. They want to see the every day life of something that wants and needs. To them, you are absolutely fascinating.
Next time you see something out of the corner of your eye, don't fear. Act like they're not there, and go about your daily life. Just know that they are always there.