Edge cases is where every legislatively mandated process I've ever administered has failed hard. The laws and regulations I was administering worked well for 99% of clients.
But if you were in that 1%, shit sucked, sorry.
Two examples:
1) You're a single parent working part-time as a legal secretary, and in receipt of some form of social welfare payment to ensure you and your children don't end up in hardship.
You are offered full-time hours! Yes! Except because you hit the boundaries/limits/edge cases in the legislation, your net income will only increase by $30 a week, because your income tested supplementary assistances will decrease as your earnings do.
Now, the legislation in play here, ensures social welfare and works okay for 99% of people (when I say "works okay", I mean, gives them money, and doesn't disincentivise work). But that income testing bites you as you approach the edge of the income curve.
2) You want to go hunting in a national park managed by the Dept of Conservation. The usual hunting permit requires that you only use centrefire rifles - rimfires and shotguns are totally banned (to prevent hunting of native birds, especially the tasty fruit fed kererū/kūkupa/wood pigeon[0]). However, you want to hunt red deer and chamois, with a crossbow.
The policies at the time don't account for crossbows (and this was before bow hunting was as common place as it is now). So the department defaults to "No".
In both situations, the broad rules work well for 99% of users. But for the 1% it sucks. The key to the 1% is human discretion and agency.
Good systems, whether legal, business process, or algorithmic, always allow for a human to override. Bad ones don't. "Computer says no" style.
(On the crossbows, a ranger (my Mum, I'll be honest) went into bat for the hunter in question, to determine what was needed for "no" to become "yes", and well, now there's a policy that determines the minimum draw weight for a crossbow to be considered humane - and no barbed or exploding bolts allowed! [1])
[0]: https://www.doc.govt.nz/nature/native-animals/birds/birds-a-...
[1]: https://www.doc.govt.nz/parks-and-recreation/things-to-do/hu...