Strong fiction (or poetry for that matter) will use allusions so that the fiction works on both levels. Readers who get the allusions gain a richer understanding of the work, but those who don't can still follow the story and be entertained or enlightened by it. I often think of allusions as a kind of hypertext, linking the reader to another tradition or literary history. I can also think of poems, like "The Wasteland" (see below), in which the poet was practically sampling other works, the way DJs sample other songs. However, allusions can also be quite subtle. For instance, Shakespeare's influence on literature in English is so strong that we often make allusions to his plays without being aware of it.