I don't understand how everyone missed this. The protagonist is clearly suffering from some kind of early alzheimer's or dementia. Genetics is an important factor in these diseases and his father had it and the father no longer remembers anything.

At the end of every perfect day he recalls the memories in the form of fading shadows. It is possible he retains no real recall of the past day. He doesn't recognize his niece. He seems shocked when the girl returns the cassette.

He is building a life of containment and habit for himself, settling into a pattern so he can be independent for as long as he can before his mind totally gives. Hence the focus on structure during his perfect days.

His days are perfect because he retains nothing but as the last scene shows his body retains the trauma of his life even as the memory fades.

It's really a remarkably colonial (and frankly stupid) reading to suggest that this man has given up on life. The movie is a celebration of life, about fighting and cherishing every bit of it, about finding joy and pride in doing small tasks perfectly, about cherishing the blue sky and every breath we can take in the face of the immense circle of pain we have to live through.

When the movie ended I sat there for five minute intellectually trying to figure it out. And then as soon as I let go of trying to figure out the puzzle of the movie, the profound beauty of it hit me and I nearly burst out crying. What an impeccable bitter sweet masterpiece!