PERSISTENT IDENTIFIERS:WHAT IF?

"There was a great exhibition by Sandro Botticelli in Florence only a few years ago. It was the first time so many of his works were collected in one place and I remember reading very positive reviews about it.
But … I can't find the information about this event any more … I type the correct URL and what I get is '404: not found'. It is so annoying considering the event is so recent. I wonder what we'll find in ten years' time."

"You wouldn't have this problem if Persistent identifiers had been used to refer to that exhibition!"

"Persistent? What are you talking about? Everything is so volatile nowadays … anyway, what do you mean by 'Persistent Identifiers'?"