A coordinate can be checked. It is still not a wall.
Play a note outside the key and everyone in the room hears it. Not the trained ones. Everyone. People who cannot name a single chord will wince within a beat.
Now watch a good player do it on purpose. Same note, outside the same key, and nobody winces. They lean in.
The listener cannot tell you the rule. They can absolutely tell you the difference between a mistake and a choice.
Which tells you something about boundaries. They are not walls. A lot of the best work sits just outside the line, close enough that the line is still visible. Never outside, and the work is correct and forgettable. Outside without knowing where the line was, and it is simply wrong.
So a system that enforces hard limits buys you safety and quietly costs you the top of the range. Everything defensible, nothing memorable.
You cannot deliberately break a rule you have not stated.
If the boundary lives in someone’s head, every deviation looks like an accident. It gets smoothed away on the route to publication by somebody being careful. The transgression never survives the review.
Writing the boundary down does not prevent crossing it. It is the only thing that makes crossing it legible as a decision.
Which raises the obvious question. Somebody has to decide when outside is better than inside.