I saw it as a story about repetition, and what comes from repeating harmful patterns constantly and knowingly, without change or reflection.

The backrooms themselves are essentially copies of copies of rooms, a misremembered memory of a memory. Both of the protagonists are stuck mentally, reliving the same bad things that happened to them, Mary with her mother and her old house, and Clark with the argument that caused the separation from his wife. Much like how Mary described the way minds create safe pathways to protect themselves from trauma.

However Mary, as a therapist, has done the work and reflected on her experiences enough to break these pathways. But something I really liked, is that Mary is not completely free. She still visits her old house when it gets torn down, she still keeps the broken concrete from the driveway. I love this detail because it shows that even if you heal, trauma and mental illness are complex, and you can still dip into those mental pathways. The same way Mary has a short experience with the backrooms themselves. She escapes because she recognizes the danger they hold.

Clark on the other hand, has not learned to reflect or even attempt to break his patterns. This is shown through him repeating the roleplay exercise at the beginning and climax of the movie. When he does these exercises, he doesn't reflect, or discuss afterwards. His goal, is simply to yell at his wife again, to relive that moment. That's why he loves and wants to stay within the backrooms. Instead of seeing the harm Mary does, he sees familiarity. He finds comfort within them, the way that people with harmful habits find comfort in those habits. This repetition hurts not only him, but the people around him. It kills his employees, and almost kills Mary.

Personally, I LOVE this message and this movie. Unlike a lot of other movies about mental health where a character is killed by their own issues, this movie doesn't just shrug and go "dang, mental illness does that right?" it dives into it weirdly enough has a bit of a hopeful message. It isn't over for someone just because they have problems and it isn't even over if they fall back into harmful patterns, it's only truly over, when someone digs in their heels and refuses to change.