Refuse, don't guess

The rule that ambiguity is an error to raise, not a heuristic to apply. A label that appears zero times or twice, a date that parses two valid ways, a missing expected column: each stops the build and names what was ambiguous. Guessing past ambiguity is how wrong numbers get published.

Principle 3 · Refuse to guess

Where does Refuse, don't guess come from?

Principle 3 of the Kymira doctrine, Refuse to guess. Refuse, don't guess is the name the doctrine gives to what that principle requires in practice.

What failure is Refuse, don't guess named after?

The date that parses two valid ways. 4/9/2026 is April or September depending on a locale the file never states, and both parses succeed.

What does it look like on a real file?

Two accounts share a name and carry no stable id, so the join stops and names the collision instead of picking one.

Not for

Not a licence to refuse everything. A refusal names precisely what was ambiguous and what would settle it.

Nearest terms

Filename lieA file named by the system that produced it rather than by what it holds Period from contentsEstablishing which period a file covers from the rows and the pre-header metadata inside it,...Join coverageThe share of rows that found a match when a table was joined to a reference

Last updated 2026-09-02 · Dylan, founder · one of 40 terms in the Kymira glossary, each one named after something we watched go wrong in a real build or in our own audits.

Get the free skill → The doctrine The failure catalogue