This goes deeper, since understanding grep regexes involves understanding quoting.

This means not only how regexes distinguish between literals and control characters, but how the shell distinguishes and passes on characters to the regex that grep receives as an argument.

I think regex quoting is one of the major stumbling blocks of comprehension.

Even after decades using regexes, I still stumble (especially when my regexes are used in the shell, in emacs, in python re.match, etc...)

Friedl's "Mastering Regular Expressions" is one of the best books I've ever read and started my Unix journey via Perl and Emacs.

Which rather reinforces the point of the headlined article: People actually learn a lot of stuff when they start out from tutorials, guides, handbooks, and whatnot; not from purely reading reference doco. I started out with books, too. Later people would have started with the likes of TLDP.

I suspect that the author is right that most people started with guides/handbooks/tutorials, even the ones who later on convince themselves that they only read reference doco.

O'Reilly's bestiary had an exceptional line-up of Unix classics in the early 2000s.