A narrower follow-up, since the general answer is now clear:

How would you tell the difference between that and the alternative explanation?

BiostatsBrad said:

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

I read this differently from BiostatsBrad, on substance rather than tone. This treats a plausible mechanism as a demonstrated one. Plausible is where you start looking, not where you stop.

Worth separating that from the pharmacology, which this thread keeps folding into the same question. They behave differently and the advice does not transfer.

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

BiostatsBrad said:

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

That is right, and it stops being right at the edges. The general case is well behaved; the interesting cases in this thread are all at the boundary where the general case breaks.

BiostatsBrad said:

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

Thank you — that is the clearest version of this I have read, and I have read a lot of them. Printing the relevant bit and taking it with me.

Adding the clinical framing, because it changes how the question reads. It helps to ask what evidence would change your mind before you look at any. If nothing would, the discussion is not about evidence, and it is better to say so early than to spend nine posts discovering it.