The concept of the picture plane cleared up how I should be thinking about when parallel lines converging. I had the idea that lines going away from the viewer should converge - but after watching the picture plane videos, I was wondering why the vertical lines weren't coming together if they were going up/down away from the horizon line. My understanding of convergence was incomplete and I wasn't considering the paper as a window to the world on the other side. After a good bit of thinking while holding a napkin (as a window) with a vertical/horizontal pencil up in front of me, I think I got it. Thank you for the insight you're sharing with these videos.