I couldn't "attach" the triangular-pyramid to the square-pyramid because I had made them different sizes and then accidentally distorted the triangular pyramid when I enlarged it, so it didn't fit on the faces of the square-pyramid. I didn't realize that was what I had done until I looked at the linked image of the rhombus. This is definitely an unexpected way for my mind to malfunction.

I have always been flummoxed by the fact that I can imagine any image in high detail, yet drawing is difficult. When I was younger it seemed like I should be able to just "project" my mental image onto the paper and then "trace" it, but this doesn't work. I can draw fairly well, but that's due to practice, not any kind of image projection. In fact, drawing and imagining images feel like completely separate systems.

ETA: Pain! I find it very difficult to imagine pain in most circumstances. I think one's capacity for empathy may be partly linked to their ability to imagine pain.