A policy’s real shape appears in the ordinary case its author did not imagine.

Rules are written from a picture of a typical person, and the picture is always narrower than the population. Their real shape only becomes visible when somebody turns up whose life is perfectly ordinary and simply not the one imagined: two jobs, no fixed address, a carer, a different kind of body. These are not exotic cases. They are ordinary lives that were left out of the drafting.

If you write or apply any rule, test it against a specific real person rather than an average one. Ask who would have to explain themselves to satisfy it. That question finds more than any amount of rereading.