The type of incest depicted in A Simple Favor doesn't fit these typical molds. Viewers are supposed to believe that Stephanie and Chris are two adults who chose to be in a relationship — but why? Yes, it's a major plot driver, as Stephanie ends up being blackmailed with this information, but surely the book and film adaptation could have come up with a more realistic reason. Maybe it's to make Stephanie appear complex, maybe it's simply for shock value, since incest is one of the most controversial types of consensual relationships that anyone can ever enter. But on top of all the other shockers in the movie, the incest element really wasn't necessary; it ends up being just another ridiculous aspect of A Simple Favor's storyline, one that doesn't add any real emotional or narrative value to the plot, and probably wouldn't happen IRL.