When I was interviewed for the job I currently hold, my boss-to-be asked several questions from a list. The first was "what is grep". The others were similar in their difficulty.

When I remarked (after the fifth or sixth such question) that these were not difficult questions, she noted that they were not easy for everyone!

The questions were meant to smoke out someone whose actual skills and knowledge were markedly at odds with what the CV appeared to claim, and some of the candidates for my position were apparently Not Up To Snuff. The questions were not meant to be trick questions, or tough questions. If they were difficult, it was a bad sign for the candidate.