Greek mythology: Sisyphus was the king of Corinth who was punished in Hades by having to repetitively roll a huge stone up a hill only to have it roll back down again as soon as he had brought it to the summit. This mundane task is also seen as a metaphor to laborious contemporary life and its repetition of modern society. This perpetual task is where the term "labour of Sisyphus" or a "Sisyphean task" derives.
Netflix Canada list this as Sisyphus actually a different Korean series about a cat.
The flight designator for the plane in the first episode, Air Koreana JH007, is eerily similar to the flight designator of the 747 shot down by the Soviet Union in 1983, KAL007.
Cho Seung-woo (Han Tae Sul) and Tae In-ho (Eddy Kim) were both in Stranger (2017) and played Hwang Shi Mok and Kim Byung Hyun, respectively.
Tae In-ho (Eddy Kim) and Kim Byeong-cheol (Sigma) were both in Tae-yang-eui hoo-ye (2016). Playing Hospital chairman Han Suk Won and Lt. Colonel Park Byung Soo, respectively.