Bluma Zeigarnik, a Russian psychologist described this effect in 1927 in her paper "Das Behalten erledigter und unerledigter Handlungen" later translated as "On Finished and Unfinished Tasks." This Zeigarnik Effect, as discussed in previously, indicates that an incomplete task or narrative is retained in one's memory until it can be resolved. By telling a story with appropriate emotional triggers and leaving it incomplete in such a way that the only way to achieve satisfactory closure is for the audience or target to take a specific action is a way to exploit this effect (not unlike the rhetorical use of enthymemes). This unknown partial pattern is also the basis of hermeneutic code, and both the semic and hermeneutic codes work because of the brain's pattern recognition and its desire to close the figure. Narrative is a primary pattern to the neuropathology of conscious thought. It is a pattern of linear causative relations that is particularly compelling once recognized as such. Cliffhangers, ongoing serialized narratives, and nested NLP commands all involve this kind of incompleteness that engages memory and cognition toward a specific end. Music in commercials often uses this technique as well, and even ring-tones represent this kind of incompleteness and looping to alert the phone's owner to incoming calls.
In this age of the Internet, we are seeing a new narrative structure, the modular or non-linear narrative, becoming more prevalent than ever before. We can locate an audience and distribute bits of narrative in the form of a kind of conceptual puzzle piece in places where we know they will be observed. All the fragments must connect with some other fragments, and it must be possible to follow these pieces back to an offer of completion, while still retaining some value to the audience in and of themselves.
Likewise, the whole pattern must somehow be of value to the audience as a whole. As long as each piece is consistent, the non-linear storyteller is building a corresponding pattern in the mind of the audience. As they discover their own path through the web of synchronicity they will come to the source of the narrative because of a compulsion to complete the puzzle, fill in the blank, track down the meaning, or otherwise engage the media because of its discontinuous elements. Because of the involvement of the audience in actively gathering these fragments, it is best to over-deliver on audience expectation, should they successfully re-assemble the narrative. That way, those who make up that network will be more liable to look for the storyteller's next transmission.