I’d like to ask the good people of this community that, if you do know the solution or figure it out, that you not share the answer here. Feel free to announce your success, but there’s something to be said for discovering the answer completely unaided, even if it takes years.
It’s embarrassingly obvious once you see it though.
I love puzzles like this—the rule always seems obvious after you see it. It’s satisfying when something that sits in the back of your mind for years finally clicks.