Do you say that seeing is believing and trust only what you see? Yet you know that the train tracks remain the same distance apart even though they appear to converge in the distance.
Windows, doors, and walls have parallel edges but drawings showing them this way look crude and flat. The appearance of such structures depends on perspective and a knowledgeable illustrator will use vanishing points to draw perspective correctly. So things don’t look the way they really are. You should be cautious about believing even the things you see, but if you believe me I will reveal to you things unseen.