Well, I am pretty confident that the vast majority of programmers do not know both a functional and a purely procedural language. In my book, "knowing" a language entails having used it in some significant piece of software at the very least. Most programmers absolutely have not done this in ANY procedural or functional language, and very few have done significant work in both.

I guess my issue with these all-too-common HN "things everyone should know" posts is that inevitably 99% of programmers don't know all the things everyone "should" know. If you took the posts at face value, you would feel very inadequate.

A more appropriate title would be "Things I know. Look at how awesome I am!"