Its a beautiful and moving story, but in part, a DISINGENUOUS one. According to the narrative, after first seeing the octopus he has the idea that "there is something to learn here" and wouldn't it be interesting if he were to come back every day. What is NOT said is that he must have also had the idea, and intent, to have a documentary made of him doing this. We know this because the film has a "day counter" which shows the progression of the almost year of the film. The day counter starts "Day One".
So a more honest and transparent prelude to the story would have included the fact that he set out to make a documentary from the beginning.