Blair Witch ending - why is it so disturbing?

The scene with Mike standing in the corner - why do you all think it disturbed people the way it did? I saw it at the movies when it first came out and still have issues whenever I see ' that' screenshot. I'm not sure why .... I think I just had an overwhelming feeling of dread....things that can't be 'explained' easily in movies and leave things more to my imagination seem to really disturb me. How is it for everyone else?