According to a popular picture, some beliefs are justified by "seemings": under certain conditions, if it seems to you that P, then you are justified to believe that P, without the assistance of other beliefs. So seemings provide a kind of foundation for belief, albeit a fallible kind of foundation.
But most of our beliefs are not justified by seemings (or by beliefs which are justified by seemings, etc.). I once learned that Luanda is the capital of Angola and I've retained this belief for many years, although I rarely think about Angola and thus rarely experience any relevant seemings that could justify the belief.
At this point, one could appeal to merely possible seemings: my belief is justified because it would seem to me that Luanda is the capital of Angola if I were to attend to the question. But (a) my belief is justified even if that counterfactual is false, e.g. if for a short time, due to a misconfiguration in my brain, attending to the question would make me unconscious. This suggests it's really the categorical ground of the disposition that does the justificatory work, and that ground isn't a seeming. In any case, (b) it seems odd that an actual belief could somehow be justified by a merely possible seeming.
A better response is to say that if at some point a belief is justified (directly or indirectly) by a seeming and thereafter retained, then the (defeasible) justification is retained as well: no new seemings are needed.
OK. But now consider this scenario (based on a scenario I heard from Luca Moretti).
Looking outside the window, it seems to you that it is raining; you come to have the justified belief that it is raining. Then I draw your attention to the sceptical possibility that you might be halluzinating the rain. You are concerned. "Right", you think, "if I were halluzinating the rain, it could seem just like that! So maybe it's not raining!" Arguably, you're no longer justified to believe that it is raining. If you're epistemically blameless, you therefore drop your belief. In the meantime I've closed the curtains and we start talking about other topics. The sceptical scenario fades out of attention; soon you're no longer bothered by it at all, and it would take some effort for you to bring it back to mind.
At that point, would you be justified to believe that it is raining? Arguably yes. The destructive effect of sceptical thoughts on justification seems to be temporary.
So it would be OK for you to believe once again that it is raining. But where could that belief come from? Not from any relevant seeming, because it no longer seems to you that it is raining. (There's no relevant perceptual seeming, and since you're not attending to the question there's also no mnemonic seeming.) Nor could the belief be inferred from things you already believed before you had it. The belief would apparently come out of nowhere, as a kind of neurological fluke. But such a belief could hardly be justified.
Something else must survive the sceptical episode.