A large part of Boyhood's strong appeal is how all the actors on screen, particularly the children, are ordinary humans growing older over a period of 12 years.
That dimension of time gives the work a core of reality, its 19-year-old lead actor Ellar Coltrane tells Life!, and that is the key to its emotional power.
At the start of the family drama, Coltrane (real name Ellar Coltrane Kinney Salmon) is six. Events are seen through the eyes of his character, Mason, and the film ends as he heads to university.
If film-maker Richard Linklater had shot the film in a month, using actors of different ages, the result could never have been as compelling, Coltrane says.
"There is something uncanny about the way a person changes. To see time passing, to see actors gradually change, it's very human and it draws people in," he says.
When he spoke to Life! over the telephone from the United States last month, he had watched the film in its entirety several times. Seeing himself on screen grow from an average Texas boy to a moody, sensitive teenager to a more confident young adult is never a comfortable experience. The primary emotion is fright.
"It put the fear of God in me," he says with a laugh. "To see so much of myself is a lot to take. The fear has worn, but it's still weird. But now, as I am able to experience the film more, as a whole, I'm seeing more of what Rick (Linklater) was doing," he adds.
There has been a lot of interest on the arthouse film circuit as to how much the film's story overlaps with that of Coltrane's own life. After all, Linklater consulted Coltrane and his family while shaping the story over the decade-plus production period.
While Coltrane did live with a stepfather for a period - the film shows the family working its way through a succession of poor spouse choices made by the mother (played by Patricia Arquette) - the finer details (such as the Harry Potter fanboy period) come mostly from Linklater's imagination and personal experience. This work is by no means a Coltrane biopic, even if the 12-year time frame might give that impression.
"I actually wasn't a Harry Potter fan. The stuff with the stepfathers, if anything, is pulled more from Rick's life. Most of the story is shaped around his life," he says.
Where Coltrane's private life and personality had seeped into Linklater's script can be glimpsed in the small moments. "Most of my input is in the situational dynamics, between me and the people in my life, in the way I was talking to my parents or how I would talk to a girl I was meeting for the first time," he says.
For example, there is a scene in which Mason gives a monologue about how among his friends, too much life is lived to score points on social media. That was drawn from one of the many conversations that he and Linklater had as the writerdirector worked on the screenplay, with the day's scenes usually written just before shooting.
Coltrane was never shown footage until photography was complete so that the character of Mason would not affect the actor as he matured - life was not allowed to contaminate art and vice versa, both for Coltrane's well-being and for the sake of the film.
The chronological slant of the project, reminiscent of The Truman Show (1998) and the rise of reality television in recent times, bestows a truthfulness that the film would not otherwise have. Coltrane is aware of how Boyhood plays with the line separating fact and fiction.
"It has this documentary quality, and it chronicles our physical changes, and the world changing, and of me up there. There is a lot of me in the character of Mason.
"But at the time, this is a crafted thing, a thing that I took part in crafting. It's a direct representation and it's also an artistic representation," he says.