I was reading directions on a box to find out which direction I should push a lever to make <whatever> work. The directions used a triangle (like this ▷) to indicate where to push.

For no adequately explained reason, I was puzzled. I couldn’t figure out if the triangle was pointing to left and up or left and down.

I bemoaned the sense of anyone who’d use an equilateral triangle to indicate direction. A equilateral triangle could easily be pointing to 3 directions: up and left, down and left, and …

Did you ever find yourself staring at a picture of a vase and then it unexpectedly becomes a picture of two faces?

… then the triangle was pointing to the right! The directions were pointing to the right.