Filename lie

A file named by the system that produced it rather than by what it holds. A file called weekly_sales.csv may contain last week, another account, or both. Never compare a filename derived value against itself, which is a test that passes every time and proves nothing about the contents.

Principle 4 · Filenames lie

Where does Filename lie come from?

Principle 4 of the Kymira doctrine, Filenames lie. Filename lie is the name the doctrine gives to what that principle requires in practice.

What failure is Filename lie named after?

The filename that lies about the period. A file called Q2 carrying July rows. Headline the file and the quarter is wrong.

What does it look like on a real file?

A file named for the second quarter whose rows are all dated July would have put the wrong period in the heading.

Not for

Not a claim that filenames are useless. They are a hypothesis to test against the contents, never evidence in themselves.

Nearest terms

Period from contentsEstablishing which period a file covers from the rows and the pre-header metadata inside it,...Title lieA cell in a file's pre-header that looks like identity evidence but asserts nothing: an...Refuse, don't guessThe rule that ambiguity is an error to raise, not a heuristic to apply

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