The information essential to literacy is rarely detailed or precise

From E.D. Hirsch's Cultural Literacy.

Our children can learn this information only by being taught it. Shared literate information is deliberately sustained by national systems of education in many countries because they recognize the importance of giving their children a common basis for communication. Some decades ago a charming book called 1066 and All That appeared in Britain. It dealt with facts of British history that all educated Britons had been taught as children but remembered only dimly as adults. The book caricatured those recollections, purposely getting the "facts" just wrong enough to make them ridiculous on their face. Readers instantly recognized that the book was mistaken in its theory about what Ethelred-the Unready was unready for, but, on the other hand, they couldn't say precisely what he was unready for. The book was hilarious to literate Britons as a satire of their own vague and confused memories. But even if their schoolchild knowledge had become vague with the passage of time, it was still functional, because the information essential to literacy is rarely detailed or precise.