Some lessons arrive early and stay for decades. One of mine came in 1975, delivered by Michael A Jackson1 in the calm, almost off‑hand manner he used when he was about to rearrange your thinking. He described a tiny function — two digits in, square root out — a domain so small you could close your hand around it.
On paper it was perfect. One hundred possible inputs. One hundred known answers. A closed world. A finished thing. But Jackson never trusted finished things. He asked me to imagine the implementation rather than the specification.
The code, he said, remembered every input it had ever seen, and the answer it once returned. On each call it searched its private ledger. If the number was already there, it handed back the stored value. Only new numbers triggered the real calculation.
The calculation path was correct. The lookup path was wrong. The result was a creature with immaculate first impressions and a treacherous memory. The first call for any number was right. Every subsequent call was wrong.
A black‑box test suite — one call per input, no repetitions — would pass in triumph. One hundred green ticks. One hundred matches to the oracle. A perfect illusion of correctness. The fault would remain untouched, unprovoked, unseen.
Jackson let the silence sit for a moment, then offered the line that has stayed with me ever since: “It doesn’t qualify as a method unless it tells you when you’ve reached the end.”
That was the hinge. Data Analysis - Third Normal Form, black‑box testing, any ritual that promises certainty — none of them tell you when you’ve gone far enough. They tell you how to proceed, but never when to stop. They offer procedure without judgement, motion without completion.
Modern systems only deepen the difficulty. They accumulate histories no test suite can exhaust, states no human mind can hold, interactions no single perspective can illuminate. Pure human effort reaches its natural limit. Pure machine effort, confined to black‑box observation, inherits the same blindness that Michael, with that tiny, treacherous function, recognised.
The only coherent path forward is collaboration: human judgement and accountability joined to machine scale and persistence, both permitted — and required — to look inside.
The box was never black. We merely pretended the darkness was a virtue. Michael A Jackson showed me the hinge in 1975. The end is not where the ritual stops — it is where understanding begins.