I'm trying to understand where they're coming from. What is it that they believe, and why they believe that.

Where they are coming from is an irrationally-held POV they can not comprehend.

If it was rational, then they--by definition--could not have that POV.

What/why they believe is irrational, so you end up with an Escher Staircase:

'Escher's staircase refers to impossible, continuous loops of stairs seen in < M.C. Escher's lithographs like "Ascending and Descending" (1960) and "Relativity" (1953), based on the Penrose stairs idea by Lionel and Roger Penrose, where figures walk forever without changing elevation. These optical illusions defy 3D reality, creating a paradoxical sense of endless ascent or descent through clever perspective and impossible connections, often symbolizing life's circular journeys or logical puzzles.'

Search for "Escher Staircase" and you will find a number of them displayed.

This video shows how a real-life Escherian staircase works in a different geometry:

YouTube: How Does a Real-Life Escherian Staircase Work? (The Action Lab) (warning: ad intro to Youtube)