When I took a class on circuits, as in electrical circuits, my fellow students nicknamed the class Magic. Since it lasted two semesters, we called the classes Magic 1 and Magic 2. The class got the name when the instructor started talking about an electron running backwards in a wire. We simplified it to say: You throw a switch on the wall and light comes on — it’s magic!
I don’t recall any class on plumbing referred to as magic. But if there was, it would have to be the subject of venting. To many, venting is magic because it protects the trap seal. However, most are not sure how the venting system works. So rather than studying the scientific details, it is easier to make things up.