He has other theories about where the idea came from: One is that a lot of actors had been asking him to write a play, and since "the stage is a limited space, I was trying to come up with a story that I can tell with just two homes: one poor and one rich." He also described himself as "very fascinated with the sense of 'infiltration.' When I was in college I also worked as a tutor for a very rich family, and I got this sense that I was inevitably spying on the private lives of complete strangers -- when [the son] Ki-woo first enters the the rich home [in Parasite], that's something that I experienced as well."
In Parasite, to dig his family out of their tiny, poor, sub-basement apartment life, young Ki-woo (Choi Woo sik) has his sister forge a college degree and takes a job as an English tutor for the rich Park family's daughter on his friend's recommendation. When the wealthy wife shows off her young son's "art," saying she wants to develop his talents, Ki-woo snatches the opportunity, and recommends a colleague named Jessica who, unbeknownst to his employer, is his sister, Ki-jung (So-dam Park). Gradually, the pair get their parents, Kim Ki-taek (Song Kang Ho) and Choong-sook (Jang Hye-jin), in the mix as well, carefully concocting a scheme to replace the help in the Park household with their own family members.
"We built all the houses -- the rich house, the poor house, and the neighborhood surrounding the poor house," Bong said. "Particularly for the rich house, because around 60 percent of the film happens there, we put in a lot of care into the details of the design."