When a reader becomes fully engrossed (also known as being 'immersed') in the illusory narrative world of a book, the author has achieved a close aesthetic distance.
Bullough writes, "Distance … is obtained by separating the object and its appeal from one's own self, by putting it out of gear with practical needs and ends.
An easy example in theater or film is "breaking the fourth wall," when characters suspend the progress of the story to speak directly to the audience.
William Goldman, in The Princess Bride, repeatedly interrupts his own fairy tale to speak directly to the reader.
Examples might include a director's cameo, poor special effects, or perhaps blatant product placement - any can be enough to pull a viewer out of the reality of the film.