The person designing the exception process decides how expensive being unusual becomes.

Every system needs a route for the cases it did not anticipate, and whoever designs that route sets a price. Make it short and staffed and the unusual person is accommodated. Make it long, evidenced, and repeatable and being unusual becomes a second job. The rule itself may be identical in both cases, so the real policy is in the exception process, where almost nobody looks.

If you build or run anything with rules, look at what an exception actually costs the person requesting it, in hours and in evidence. If you are the one asking, it is worth knowing that the difficulty is a design choice rather than a measure of how reasonable your request is. Naming that changes how you carry the refusals.