Although this didn't work for me, I know why it would work. The images you see aren't real images of your surroundings, as the human eye is far from perfect. This means it has to compound and edit the images from both eyes, and it makes a lot of mistakes. The disappearing box is because your brain thinks that the box you're looking at is the only box (as it cannot properly see the other) so it removes it and replaces it with the black background