Most of us were taught to pay attention to the things we did not understand. We were told to go to a dictionary when we met an unfamiliar word. We were told to go to an encyclopedia or some other reference work when we were confronted with allusions or statements we did not comprehend. We were told to consult footnotes, scholarly commentaries, or other secondary sources to get help. But when these things are done prematurely, they only impede our reading, instead of helping it.