That line is from the third Indiana Jones film “The Last Crusade” (it should have BEEN the last movie, but I digress). Indy’s teaching class and trying to disabuse everyone of the idea that archaeology is about finding treasure, that there are no treasure maps and thus — “x” never, ever marks the spot.
Of course, he gets to eat his words later in the movie when a critical discovery is marked by an “x”. Really, it’s a Roman numeral for 10, but an x is an x. Right?
I think that’s a great cautionary tale against raging generalizations. Indy wants his students to believe that archaeology is all books and only a certain amount of field work even as he knows that’s not the case… (at least in HIS universe)
Here’s the clip from the film.