Those two paragraphs contain a lot of wisdom.
I can give an example of a writer who didn't realize the limits of his knowledge: Bill Bryson wrote The Mother Tongue, and as far as I can tell, it is good and reasonably scholarly book on the English language.
However, Mr. Bryson wrote some pages about the Japanese language in the book since Japanese is indeed a good language to contrast various aspects of English with. The problem with him writing about Japanese is his lack of knowledge of the subject and the egregious errors he makes about various aspects of the language.
Those blatant errors certainly made me wonder just how careful his scholarship was with respect to other parts of the book where he talks about far more obscure topics than Japanese, which is one of the world's top languages in terms of the number of speakers and where plenty of elementary material is available on the subject. As far as I know, there aren't many sources available to cross-check his assertion on the length of time for the use of Celtic names for numbers by shepherds in Yorkshire, which Mr. Bryson states occurred up into the 20th century.
This one sentence contains so much wisdom. Remember when Rummy was laughed at and scorned when he stated there are the things we know, the things we don't know, and the things we don't know we don't know.
I need to go back to the Bible and start reading the Book of Wisdom again.