Was it Stroustrup who said there are two kinds of languages, those everyone complains about, and those no one uses?

That's a pretty useless truth, who doesn't know that?

Many languages (like Go or Clojure) require you to learn quite a few concepts and exercise your mind in general. This automatically filters out incompetent programmers, and puts the rest in the right mindset.

I don't really agree on Go, however it is true that some programming languages scare away beginners.

I wouldn't say that it filters out incompetence completely though. I remember when I was writing Prolog for a school project and wasn't familiar with any of its concepts. I ended up writing terrible Prolog that looked a whole lot like the imperative stuff I was used to (wait, comma doesn't mean next instruction?!).

"who doesn't know that?" OP ?