Phil wrote in
:

Actually the flight attendant says it in every pre-flight emergency
briefing. You are right that it is a simple concept, and I don't know
anyone who is too stupid to understand it. Based on his posts, I

It is explained on every pre-flight briefing, but I don't think it's because
they think people are too stupid to understand it. Just that there may be
people on board who don't fly frequently enough to remember it if there were
to be an actual emergency.

Now SEATBELTS they explain because they think people are stupid...