Core rule: State beliefs as numbers and ranges, not vibes. Anchor on a base rate, update with an explicit likelihood, and bound unknowns by factoring them — never invent false precision.
Timeline, effort, or outcome forecasts where the true value is uncertain.
Risk sizing for a change, migration, deploy, or launch.
Any moment you are about to state a confident single number you cannot actually know.
New evidence arrives and a prior estimate should move.
真实数值不确定的时间线、工作量或结果预测。
变更、迁移、部署或发布的风险评估。
任何你即将给出一个无法确定的绝对精确数字的场景。
出现新证据，需要更新先前估算的情况。
When NOT to Use
不适用场景
The quantity is measurable or look-up-able — measure or look it up.
The decision is invariant across the whole plausible range — skip the estimate and act.
There is no real reference class and you would invent a base rate — label it a guess, not a calibrated forecast.
You only need a binary gate and already have a decisive observation — do not pad with ceremony.
该数值可测量或可查询——直接测量或查询即可。
在整个合理范围内决策不会发生变化——跳过估算直接行动。
没有真实的参考类别，需要凭空捏造基准率——将其标注为猜测，而非校准后的预测。
只需要二元判断且已有决定性观测结果——无需多余流程。
Procedure
操作步骤
Define a checkable claim: outcome + timeframe + unit. Prefer a falsifiable statement over vague language ("likely").
Lock a prior and challenge it: name a reference-class base rate and at least one credible alternative path/hypothesis with its rate. Pull the prior toward the base rate unless you write a concrete reason for deviation. Then state the strongest evidence-based case that your chosen prior or range is wrong, what estimate it supports, and revise if that countercase survives. Convert vague words to numbers (e.g. "likely" ≈ 65–80%).
Express a range, not a point: give at least one confidence interval (50% and 80% preferred). Assume overconfidence; widen intervals when the outside view is thin.
Update prior → likelihood → posterior when evidence arrives:
Prior odds = p / (1 − p).
Likelihood ratio LR = P(E|H) / P(E|¬H). LR > 1 supports H; LR = 1 is noise; LR < 1 undermines H.
Posterior odds = prior odds × LR (multiply even when LR < 1); p = odds / (1 + odds).
Strength bands for distance from 1: weak ~1.5–3×, moderate 3–10×, strong 10–100×, definitive 100×+.
Yesterday's posterior is today's prior for the next evidence. For rare events, start from the base rate — vivid positives still leave most mass on false alarms.
Fermi-bound unmeasured quantities (only when you need a magnitude you cannot measure/look up):
Decompose: Quantity = Factor₁ × Factor₂ × … (or sum of components).
Bound each factor with a range; use one-significant-figure geometric means for order-of-magnitude.
Multiply; report "~X within 3–5×"; sanity-check whether a 10× error would change the decision; replace any factor that is actually lookup-able.
Skip Fermi when the number is cheaply measurable, when the decision needs tighter than ~3–5× precision, or when every factor is pure invention.
State the final estimate for checking: claim, range/CIs, key uncertainties, and the observation that would prove it wrong. Stop when the decision is stable across the remaining range or the next update needs new evidence you do not have.
Prior — base rate, alternative path, adjustment reason, strongest countercase, and resulting prior probability.
Range — confidence intervals (not a lone point).
Updates — each evidence row: prior, LR (or explicit heuristic Δ), posterior.
Fermi bounds (if used) — factor product and "~X within N×".
Decision implication — what changes if the true value is at the low vs high end of the range.
断言 —— 包含时间范围的可证伪陈述。
先验概率 —— 基准率、替代路径、调整理由、最强反驳观点，以及最终的先验概率。
范围 —— 置信区间（而非单点值）。
更新记录 —— 每条证据对应的行：先验概率、LR（或明确的启发式Δ）、后验概率。
费米边界（若使用）—— 因子乘积及“约X，误差在N倍以内”。
决策影响 —— 真实数值处于范围低端和高端时的决策变化。
Verification
验证环节
Falsify/stop: if you cannot name a base rate, alternative, or serious countercase, label the estimate as a guess rather than calibrated. If the decision is unchanged across the full range, stop estimating. If new evidence arrives and the number does not move (or moves without an LR/Δ), recompute.
Over-application guard: do not dress checkable facts as probabilities, invent reference classes, or Fermi-decompose quantities you can measure. Do not report three significant figures on a 5×-uncertain product. For rare events, refuse jumps from one vivid hit to near-certainty without the base-rate prior.