Diagnose
Reason from the symptoms to the cause and leave the symptom untreated; stop only when the cause is named.
Five whys: refuse the first answer, four more times.
Seen in Don Norman, The Design of Everyday Things, 1988
Try it on your work
Take one recurring physical fault (a wobble, a jam, a stain) and trace it backwards one contact at a time until you reach something that isn't itself caused by the fault. That is the cause's address. Fix nothing yet.
Write the complaint exactly as it is felt, in one sentence. Ask "what produces this?" and answer; then ask it of the answer. Stop when the answers start repeating. The repetition point is the real depth.
Take one chronic project problem and list everything that would have to be true for it to keep happening. Test the shortest item on the list against reality. You now know one true thing; repeat only if needed.
How it has been used
Reason from the surface signs to the underlying cause: the mechanic listening to the engine, the doctor reading a rash, the editor spotting the structural fault behind a weak paragraph. The move forbids treating the symptom: the deliverable is the cause, named, or nothing.
Where it leads
Grouped under Let me find out what holds up