The second opinion

In several professions, an expensive decision requires a second person to look independently before it is made. Radiologists read scans in pairs on certain cases. Aircraft maintenance requires an independent inspection of critical work. The practice is older than any research supporting it, and the research, when it arrived, supported it for a reason people often get wrong.

The obvious theory is that two experts are better than one because two sets of knowledge are larger than one. That is part of it. The larger effect is about independence. If the second person reads the first person's conclusion before forming their own, most of the benefit disappears. They are no longer checking the case; they are checking whether they agree with a colleague, which is a different and much easier question.

This is why the procedures are specific in ways that look fussy. The second reader does not see the first report. The inspector does not know what the engineer signed off. The order of examination is sometimes randomised. Each rule exists to protect the second judgement from the first.

Students can borrow this directly. Asking a classmate to check your essay after telling them what you were trying to do produces agreement. Handing it over with nothing said produces a reader, which is what you actually need.

The discipline is uncomfortable, because explaining your intention is exactly what you want to do, and it is the one thing that destroys the value of the check.