One thing is certain about Sean Penn: he is persistent.

It took Penn 10 years to get the rights to make “Into the Wild,” his latest foray into film directing. Even after that, adapting Jon Krakauer’s bestseller was an extremely challenging process, according to the Oscar winner.

“It was quite a dance back and forth because it’s not a simple story,” said Penn, who also directed “The Indian Runner” (1991) and “The Crossing Guard” (1995).

“There were complications in the family, and also a lot of balancing of sensitivities and responsibility in telling the story.”

Nevertheless, Penn insisted that the life of Christopher McCandless, the film’s protagonist, make it to the big screen, saying that audiences needed to witness McCandless’s pursuit of a meaningful life beyond the conventions of society.

“There are those who will look at this as a spoiled rich kid who ought not have to put himself and his family’s emotions in peril,” said Penn. “I see the size and the courage of his will. His need was great enough to justify it for him, and that was great enough for me.”

Penn’s own frustrations with the pressures of society also drove his desire to make the film.

“Speaking for myself as a 47-year-old who read this book when I was a little closer to the magic years of life...I’ve been having a growing frustration with what I call a lack of activism in the anti-bling youth,” he reflected.

Penn admired McCandless’s pursuit to define himself, even if it was reckless and dramatic at times. He explained self-activism as “knowing the limits to test, not getting trapped in living for comfort in all times, revealing yourself to yourself, not only feeling your life as it’s happening, but participating in it.”

After that, Penn says, it’s possible to turn outward again. “Maybe you can come back to society and contribute rather than being another ditto head in it.”

To aid Penn in realizing his vision, Emile Hirsch (“Lords of Dogtown,” “Alpha Dog”) stepped in as the ideal actor to portray McCandless.

“I saw him in “Lords of Dogtown” and the mischief in his face...I knew I could relate to that in him. His physicality and his heart, those things I could feel very comfortable with from early on,” Penn said.

Penn was looking for a total physical and emotional commitment from his actor for all eight months of production.

“Was this guy ready for it? Was he in need of it? It seemed to me that he was. It’s always a gamble because you don’t know what someone will do when you lead him into the water.”

And for this film, Penn would literally lead his actor into water. Hirsch took the challenges in stride, kayaking along the Grand Canyon rapids among other physically demanding stunts. In fact, Hirsch says, a longing for adventure inspired him to take the role.

“I had a kind of feeling, not of dissatisfaction, but a superabundance of energy that didn’t have an outlet in the way I was living,” said Hirsch. “The getting of itchy feet, the need for adventure, the wanderlust, having new experiences: that is what I responded to.”

Hirsch’s commitment to the film went further than adventure travel, however: in order to accurately depict McCandless’s emaciated state by the end of the film, he adhered to an extremely strict diet, losing 40 pounds.

“There was something about Chris’ story that really moved me, that made me take the gravity of the situation: a family lost its son,” he said of his dedication to the character. “Carine (McCandless’s sister) really wanted to make sure I was serious about what I was doing because she loves her brother so much...she made me want to tell the story as best as I was able to.”

The desire to present McCandless’s story authentically motivated Penn as well.

“When you find a story like this...you realize that the closest thing to the answer can be found in nature...[and as a director,] you can follow a trail, photograph it as honestly as you can, and hope people walk out to their own version.”

—Staff writer Victoria D. Sung can be reached at vsung@fas.harvard.edu.