Core rule: Diagnose deviations by testing causes against both IS and IS-NOT. Compare consequential choices by screening MUSTs, weighting WANTs, and exposing adverse consequences before selecting.
A defect affects some objects, places, times, or cohorts but not comparable others.
Several candidate causes remain and the contrast boundary can discriminate them.
A consequential option choice has explicit non-negotiables, competing objectives, and risks that should be compared consistently.
缺陷影响部分对象、地点、时间或群体，但不影响其他可对比的对象、地点、时间或群体。
仍存在多个候选原因，且对比边界可区分这些原因。
重大选项决策具有明确的非协商要求、相互竞争的目标，且需要一致对比风险。
When NOT to Use
不适用场景
A uniform failure has no meaningful IS-NOT contrast, or the cause is already confirmed.
One cheap observation settles the cause or one option plainly dominates every requirement.
The criteria cannot be made operational; clarify them before assigning weights.
The task is forward failure discovery for a planned change rather than diagnosis or option selection.
出现统一故障，无有意义的IS-NOT对比，或原因已确认。
一次低成本观察即可确定原因，或某一选项明显满足所有要求。
无法将标准转化为可操作的指标；在分配权重前需先明确标准。
任务是针对计划变更进行前瞻性故障排查，而非诊断问题或选择选项。
Procedure
流程
Choose the mode. Use Problem Analysis for a deviation from expected behavior; use Decision Analysis for a choice among options. State the target and do not mix scores with causal evidence.
Frame the target. For a deviation, record object, defect, location, time, extent, and impact. For a choice, state the decision, alternatives, constraints, and deadline.
Problem Analysis — build IS/IS-NOT. For WHAT, WHERE, WHEN, and EXTENT, record IS, closest comparable IS-NOT, and the distinction unique to the IS side. List changes near the first occurrence.
Problem Analysis — difference-test causes. Generate candidates from distinctions and changes. A candidate survives only if it explains both IS and IS-NOT. Run the cheapest discriminating check; stop when one verified cause explains the full boundary.
Decision Analysis — screen and score. Define pass/fail MUSTs and weighted WANTs (1–10 importance) before scoring. Eliminate options that fail any MUST; score survivors against each WANT and calculate weighted totals using the same scale.
Decision Analysis — test downside and sensitivity. For leading options, list adverse consequences with probability × impact and identify assumptions or weight changes that would reverse the ranking. Do not let a high total conceal a ruinous failure mode.
Decide or expose the gap. Return the verified cause or highest-ranked acceptable option, the evidence/score behind it, residual risk, and next verification. If no cause verifies or no option passes MUSTs, return open/none rather than force a winner.
Problem Analysis: problem statement; IS/IS-NOT matrix with distinctions; nearby changes; candidate-vs-boundary tests; confirmed cause or next discriminating check.
Decision Analysis: decision statement; alternatives; MUST screen; weighted WANT matrix; adverse-consequence table; sensitivity/reversal conditions; selected option or none.
Falsify/stop: reject a cause that cannot explain both sides of the boundary. Reject a choice if it fails a MUST, depends on inconsistent scoring, or loses under a plausible weight/risk change that was hidden.
Over-application guard: skip the full matrix for an obvious cause, trivial choice, or one-shot check. Stop when the cause verifies or the option is robust enough for the stated stakes; extra rows are ceremony.