From the documentary, "Traditionally, any monk, or gyoja who can't complete it must take their life."
From the Wikipedia article on Kaihōgyō "In the first 100 days, withdrawal from the challenge is possible, but from day 101 onwards the monk is no longer allowed to withdraw; historically he must either complete the course or take his own life. In contemporary times this is symbolic and the selection process ensures that those who embark on the practice will complete it."
It concerns only the Tendai sect of Mahayana Buddhism. I was confused as to how 1000 days, or 999 days (± the 9 days at the end in which the gyoja forgoes sleep, food and water to get as close to death as possible) becomes 7 years or 12 years. The above article on the Kaihōgyō makes more sense.
As I reflect on it, there is something to be said that the great things in one's personal life, are often only done in the dead of night and in those moments when one isn't working on one's duties like work and family.
I wonder if the practice is open to the Tendai nuns? If so is that recent? If not is that because of religious prescriptions? The short documentary left me with lots of question. Does anybody have information on the practice beyond what is on the Internet?