So, in other words: which of your core beliefs do you think has the highest likelihood of being wrong? And by wrong, I don’t necessarily mean the exact opposite - just that the truth is significantly different from what you currently believe it to be.
Probably the belief that there (isn’t) some kind of omnipotent god interested in guiding our affairs. It’s not like I’d ever be able to know. How would I cope? Pretty easily. It’d be comforting. That’s a pretty good reason to doubt it, since I’m biased in favor of it.
The thing is, I’m not picking this one because it’s the most likely one, but because all of the other “core” beliefs are either completely subjective judgments that can’t be “wrong” or are flexible enough that it doesn’t really matter.