The museum has a strict policy against having anything taped, tacked or otherwise adhered to the walls. For the sake of argument, let's make the museum an historic site and the building itself a work of art.
But you are busy with the business of teaching teachers, and have something "very important" that you really need to hang up. You remember the rule about not taping anything to the walls, but the museum never said anything about the murals.
So, yeah, you hang your "very important" poster board to the nearly 80 year old, priceless work of art in the room using masking tape. And then you seem confused when the museum director completely freaks the f*ck out.
I mean, what's the big deal, right?
(I SWEAR, WHAT IS WRONG WITH SOME PEOPLE?!)