The vast majority of pornographic movies, books and stories end with no ending; just an
iris out or a
fade/cut to black, while the action — implied or explicit at that moment — continues. There is no cessation of sexual activity, no implication that the characters have simply gone through an unusual phase of their lives — the level of sex they are engaged in is
permanent, and all the viewer can do is simply stop watching after a certain point.
Although to one degree or another this has always been the case in porn for as long as it has existed, it has become overwhelmingly predominant in the last two decades — possibly driven by the market's easy access to short, free adult content on the Internet, the producers of full-length pornographic films have shifted from at least token efforts at story-telling and plot to
PWP "anthologies". In some extreme cases, such as the work of Andrew Blake, individual scenes become little more than set pieces, with a focus entirely on the
act to the exclusion of such niceties as characterization, context, or even continuing the action as far as orgasm.
It has also been argued that the implication of a cessation to the characters' sexual activity, however temporary, would act as a
Downer Ending that would turn off the reader/viewer.
Compare
Tethercat Principle.