But norms, guidelines, heurisitics, advice, lie on an orthogonal axis to true/false: they are guides to action, not passive reflections. Their equivalent of the true/false axis are the Works/Does Not Work axis. So would adoption of the PoC work as way of understanding people, and calibrating your confidence levels?...that is the question.

OK, but that's not an adequate basis for recommending a given norm/guideline/heuristic. One has to at least sketch an answer to the question, drawing on evidence and/or argument

Yes, but that's beside the original point. What you call a realistic guideline doesnt work as a guideline at all, and therefore isnt a a charitable interpretation of the PoC.

Justifying that PoC as something that works at what it is supposed to do, is a question that can be answered, but it is a separate question.

namely, noticing and throwing away any initial suspicion I have that a comment's wrong, and then forcing myself to pretend the comment must be correct in some obscure way.

Thats exactly what I mean.

What specifically would I have done if I'd treated the seemingly patently wrong comment as cogent instead?

Cogent doesn't mean right. You actually succeeded in treating it as wrong for sane reasons, ie failure to check data.