SleepDoc_PDX said:

Say what you would expect to see if you were wrong, before you look.

That holds where the measurement is reliable. Where it is noisy — and a lot of what gets tracked here is noisy — the same reasoning produces confident nonsense.

Correct me if the detail matters more than I have assumed.

SleepDoc_PDX said:

Say what you would expect to see if you were wrong, before you look.

Saving this. It is the first explanation that did not require me to already understand it. Printing the relevant bit and taking it with me.

From the other side of the consultation, briefly. The version of this that has an answer is narrower than the version being asked. Narrow it and it becomes tractable; leave it broad and the thread will produce nine confident and incompatible replies.

rachel_ABQ said:

The version of this that has an answer is narrower than the version being asked.

Same pattern here, and in the same order.

Closing the loop on my own question.

Update — I was wrong in the opening post, specifically about the direction. Correcting it here rather than editing it away.