Googled around, I love this articles top quote:
Based on the movie’s trailers, you might have thought you were getting a highbrow take on a cabin-in-the-woods movie, with an unknown terror waiting to jump out at any moment. What you got instead was a dark, deliberate rumination on what it means to be human in a violent, unstructured world.
http://www.vulture.com/2017/06/it-comes-at-night-why-are-horror-trailers-lying-to-us.html
Um, no. If you had even half a brain you knew this movie was more than some creature in the night and that the two families(?) begin to distrust each other and how fear takes hold, makes people do rash and crazy things, etc etc etc.
I'm not even one of those "I knew the ending 5 minutes in" types.. far from it. But it's not hard to tell this movie was deeper than a monster-flick in the woods. Who thought otherwise??