We once read a book called "Feed" in high school - a ham fisted anti-capitalist book. Wherein citizens are 100% connected to an internet like service that only exists to sell them products. 90% of the class couldnt get it. Even when the teacher sat down and explained the entire plot of the book they still couldnt wrap their head around it.
56% of Americans are below the literacy level needed to interpret complex information from a text, which I read as 60% of Americans can't understand metaphor and 90% can't understand a subtle one.