Custom is only a record of what nobody has asked for yet, and asking is how it gets tested.
A rule nobody has challenged feels, from the inside, exactly like a law of nature. That feeling of certainty keeps a person from drafting the request, the missing request produces no ruling, and the silence gets filed as further proof that the boundary is real. Fences maintain themselves out of the evidence they prevent from existing.
The request was the experiment, and it only had to run once. What gave way was inherited practice rather than God's justice, and until someone asked, the two were indistinguishable from below. What has never been done looks exactly like what cannot be done, and an attempt is the only thing that separates them. The cost of never making one is a lifetime spent obeying a limit that would have moved at the first honest question.