Exception blindness

A setup that handles the ordinary case perfectly can fail silently on the rare case, and because nothing ever alarms, you keep trusting it.

You built your dad a medication routine that finally works. A Sunday-night pill sorter, a pharmacy auto-refill, a phone alarm at 8am. For seven months it runs clean and you stop thinking about it. Then his cardiologist halves the dose at a Thursday visit, and the following Sunday you fill the tray from the old bottle, at the old count, because that is what the routine does. Nothing beeped. Nothing looked wrong. The tray looked exactly as right as it always does.

Exception blindness is when a setup handles the normal path so well that nobody notices it has never met the unusual path. The tell is comfort with no evidence: you cannot name the last time it caught something, and you cannot name a case it refused. What it costs is a wrong answer delivered with the same calm as a right one, for as long as it takes a person to independently notice. The smallest correction is to write down three real exceptions this thing has never seen, a dose change, a travel week, a pharmacy backorder, then run one of them on purpose and watch whether it errors visibly or just proceeds. Add one loud checkpoint where it went quiet. This is a false alarm when the mistake would be obvious and cheap within a day, in which case exceptions surface themselves.