In the image I attached you see a cube (made by Blender). The edge 1 is smaller than edge 2 and 3. I expected that the edge 2 and 3 should be shorter than the edge 1 because as the parallel lines go away from the edge 1 they should converge and hence the edge 2 and 3 should be shorter. What am I missing?
An elementary sight line drawing puts the things to their places:
O is the observing point. The red sight lines 3a and 3b show the ends of edge 3 on the green image plane. The blue sight lines 1a and 1b show the ends of edge 1 on the green image plane.
The angle between 1a and 1b is smaller than the angle between 3a and 3b. Thus the apparent length of edge 1 is smaller than the apparent length of edge 3 (or 2).
This is only the side view. If you make the same drawing but as seen from the top you will see that the ends of edge 3 (and 2) have also sideways distance, but the ends of edge 1 haven't it. That makes the apparent length difference even bigger.
What's missing: some practicing to construct a perspective drawing when the observer's point (=the station point, as they often say) the image plane and the top and side views of the whole constellation are given.