How is the first line of Pride and Prejudice "It is a truth universally acknowledged..." an example of authorial intrusion?
Authorial intrusion describes when an author sort of steps away from the story to address the audience directly. It has the effect of making the reader less of an outsider to the story and establishes something more like a one-to-one relationship between author and reader. It lessens the distance between the two. The first line of the novel, "It is a truth universally acknowledged, that a single man in possession of a good fortune must be in want of a wife," is so famous, in part, because of its irony. Austen infuses such irony throughout the entirety of the novel, and she uses it to help us understand that she does not agree with such a statement.
Further, this kind of irony allows us to ascertain that she takes serious issue with the way the marriage market, in general, works. Consider the choice of someone like Charlotte Lucas: she can either marry an idiot or run the risk that she will become a burden and embarrassment to her family. Therefore, one could read this line as an example of authorial intrusion because Austen is using irony to show the reader that she disagrees with a statement such as this as well as alerting us to the fact that this text will vigorously employ irony to skewer common attitudes about everything from marriage to women's reading.