I wrote this story for the /r/nosleep subreddit. It didn’t do well. Here’s the URL:

https://www.reddit.com/r/nosleep/comments/7gnbyf/what_the_black_square_means/

I think a lot of good lessons came from this. Scroll past the story to get straight to my lessons learned (with spoilers).
I came to this forum a few weeks ago looking for actual help with insomnia. But you all expected a scary story from me, when all I wanted was some help. Well, here’s your scary story, and the source of my insom...