This is essentially what (might be) happening here. Harry has opened Box B and found a dead Hermione inside. That’s set and done. Assuming that he has reason to be believe that Box A will help him more than it will hurt him on average (and won’t contain, say, a dead/mindless/insane Fred and George), he has no reason not to open Box A.
Are you describing Transparent Newcomb’s problem? If so one should still one box when you see that the large box is empty. (I am not sure whether this maps precisely to the marauder’s map issue, I haven’t read the relevant chapter.)
Are you describing Transparent Newcomb’s problem? If so one should still one box when you see that the large box is empty. (I am not sure whether this maps precisely to the marauder’s map issue, I haven’t read the relevant chapter.)