A regression fixture that fails, passes on retry, and fails again next week is not noise. It is a disagreement between your suite and reality that nobody has been assigned to settle. The usual response, press rerun until green, teaches the team that red is negotiable. Google's engineering research found that roughly one in seven automated tests shows flakiness at some point in its lifecycle, and the widely quoted summary is 16% of the suite (Google testing research, as summarized). At that rate, a suite of 500 fixtures carries dozens of fixtures that will fail without a code change, and each one trains a reviewer to ignore a signal.
The cost is not the rerun itself. It is the attention. Flaky tests "provide no value in detecting bugs because they fail even when no bug has been introduced," and they force developers into repeated CI failure diagnosis (Trunk's write-up on eradicating flaky tests). Worse, a suite that passes 90% of the time stops functioning as a quality gate at all, because nobody can tell a real failure from the known noise (ContextQA on flaky test root causes).
There is a second, subtler cost that shows up in the humans. Review fatigue is the predictable result of "high-volume, repetitive, or unclear" review expectations: rushed reviews, rubber-stamped approvals, growing queues (CodeAnt on reducing review fatigue). A CI queue of repeat failures is the same mechanism in a different uniform. The reviewer who approves the third rerun of the same fixture in a week is not lazy; they have correctly learned that this particular red light means nothing. The fix is not to shout louder at the queue. It is to route the fixture somewhere a decision actually gets made.



