Diagnose before elaborating
Check the common, simple explanation first before searching for rare or complex ones.
Key takeaways
- What it is: Check the common, simple explanation first before searching for rare or complex ones.
- Why it works: Cognitive availability bias makes vivid, unusual explanations feel probable because they are memorable. But base rates favor common explanations: the classic medical aphorism 'when you hear hoofbeats, think horses not zebras' encodes the same logic. Occam’s Razor applied to diagnosis means starting with the most prevalent cause that fits the evidence, not the most interesting one.
- Evidence: Established clinical or therapeutic practice.
- Avoid: Jumping to elaborate explanations because the problem feels important or complex — importance does not raise the probability of a rare cause.
Why it works
Cognitive availability bias makes vivid, unusual explanations feel probable because they are memorable. But base rates favor common explanations: the classic medical aphorism 'when you hear hoofbeats, think horses not zebras' encodes the same logic. Occam’s Razor applied to diagnosis means starting with the most prevalent cause that fits the evidence, not the most interesting one.
How to do it
- 1List the top two or three most common explanations for the symptoms or situation you observe.
- 2Check whether the common explanation is definitively ruled out by evidence before escalating.
- 3Add complexity only in proportion to the evidence that demands it.
- 4Document what finding would make you upgrade to a more elaborate explanation.
What the evidence says
Clinical practiceThe heuristic 'common things are common' is taught explicitly in clinical medicine and is grounded in base-rate reasoning. Anchoring on rare diagnoses before excluding common ones is a recognized source of clinical error.
Honest caveat: In medicine, zebras do exist; the razor is a triage tool, not a reason to stop investigating when common explanations are genuinely ruled out.
Common mistake
Jumping to elaborate explanations because the problem feels important or complex — importance does not raise the probability of a rare cause.
IX Coach guides you through the most likely explanations for a personal challenge before helping you investigate rarer sources.
Practice this with IX Coach →