liberal liberate libertine liberace

Those who know not, and know not that they know not, they are fools, shun them

And here's the companion text suggesting that the reason that those who know not is the fact that they know not.

Kruger-Dunning effect

But even this doesn't explain the Domain-General incompetents. Maybe we just haven't yet stumbled across their particular Domain of Competency

Or, maybe it's something else:

1 A few words are in order about what we mean by incompetent. First,
throughout this article, we think of incompetence as a matter of degree and
not one of absolutes. There is no categorical bright line that separates
"competent" individuals from "incompetent" ones. Thus, when we speak
of "incompetent" individuals we mean people who are less competent than
their peers. Second, we have focused our analysis on the incompetence
individuals display in specific domains. We make no claim that they would
be incompetent in any other domains, although many a colleague has
pulled us aside to tell us a tale of a person they know who is "domaingeneral"
incompetent. Those people may exist, but they are not the focus
of this research.