Another problem with some people is that they don’t consciously believe (or won’t openly admit) they have absolute certainty. In their speech, they say that they doubt this and that, that they "cannot know everything" but I guess that’s mostly a trick for them to say "and neither do you." With them, one first needs to convince them that they are lying to themselves before having a talk about certainty vs uncertainty.
I’m instantly thinking about politics: there are many cases where you cannot build a clear model of what’s going on exactly in a given government, and the information is not only not transparent but also degraded with all the noise, intentional and not. I think it’s reasonable to maintain the feeling of doubt while ruminating on such topics.