One Source Is A Hypothesis
A single confident source becomes a stated fact somewhere between reading it and writing it down.
A claim from one source is a hypothesis. Somewhere between reading and repeating, the qualifier falls off and it becomes a fact that other work is built on. The fix is mechanical: mark single-source claims in the text itself, so the caveat travels with the number instead of staying in the reader's head.
Pattern
You find a claim that fits. One source, stated confidently, plausible. You use it.
By the next document it has lost its origin and become a premise. Three documents later something is being decided on it.
Why it looks right
The source was credible and the claim was specific. Demanding a second source for everything is genuinely slow, and most single-source claims are in fact true — which is exactly why the habit survives.
The qualifier also disappears through ordinary compression rather than carelessness. "One report suggests roughly 40%" becomes "about 40%" becomes "40%" across three edits, none of which felt like a distortion.
Why it fails
The failure is not that single-source claims are usually wrong. It is that the ones that are wrong are indistinguishable from the ones that are right once the qualifier is gone, and the confidence attached to a number does not decay with distance from its origin — it grows, because each repetition looks like independent corroboration.
Marketing-sourced statistics compound this. Several outlets citing each other in a circle look like several sources.
Instead
Mark the status in the text, where it survives copying:
[single source — unconfirmed] next to the claim, not in a footnoteTwo supporting rules. A strategic claim requires 2 independent sources before it is stated plainly — and independent means not citing each other, which requires actually checking. And when a claim cannot be confirmed, say that rather than dropping it: "widely repeated, no primary source found" is a genuinely useful finding, and it is the sentence that stops the next person from spending an hour on the same search.
$ head -12 one-source-is-a-hypothesis.md
$ cite one-source-is-a-hypothesis
Citation id SV-8325 is stable. It resolves at
https://stillvalid.dev/c/SV-8325 even if this artifact moves to another section,
which a bare URL does not survive. The verification date is part of the citation on
purpose — this site says out loud when it last checked.
[One Source Is A Hypothesis](https://stillvalid.dev/patterns/one-source-is-a-hypothesis) — stillvalid, SV-8325 (anti-pattern, verified 2026-08-14)