Look for the square that is the front of this box. Is it in the upper left of the picture or the bottom right? Can you see it either way? Can you see it both ways at once?
Our brain (especially the right neocortex) seeks familiar patterns in holistic ways to move through and interact with the world–or the Web. Backstage in the brain, trillions of neural networks compete to produce what we see, sense, feel, and think–projecting expectations from prior experiences, along with fears and desires.
In this case, the brain leaps from one box image to another, but wants to choose between them, not see them both at the same time. Your inner brain theatre (or cinema) projects one 3D box or the other onto the same 2D set of lines.
Also, you might shade this box, so that it’s not translucent, and imagine what’s inside that you fear or desire….