"I took it home and read it cover to cover twice," Penn told The Early Show co-anchor Harry Smith. "I just -- immediately it became something I knew I wanted to do as a movie, more than I'd ever come across before."
"Into the Wild" tells the story of Chris McCandless, played by Emile Hirsch, an Emory University graduate who gave away all his money and set out on the adventure of a lifetime, hoping to get a better understanding of his place in the world. Penn said McCandless was responding to a freedom calling.
"There was something I think woke a lot of people who read the book," he said. "And that was the way in which you pursued that, through something I had thought about all my life having to do with a right of passage. To put yourself on some kind of raw line between the potential of losing life. To have a real appreciation of life. Those things were very exhilarating to me."
Penn, who grew up a surfer, said he saw something of himself in McCandless.
"In that testing of one's self that you do in the ocean, it makes very familiar a lot of what it was that Chris McCandless felt that he had to do and why -- why he had to do it," Penn said.
"He was in the Alaskan backwoods for 113 days," he said. "I've never heard the criticism by anybody who was in the Alaskan backwoods by themselves for 113 days, about 79 of those days by choice. I respond to the kind of courage of conviction and I'm moved by it. Someone who is so clear about what it is that they need to do that they would go through that."
For Penn making "Into the Wild" was more than a just another project, it was a passion. And he hopes that audiences find the story of one man's search for self discovery as inspiring as he did.
"Facing things that we might learn about ourselves is difficult in the most comfortable of circumstances," Penn said. "But the face the most dynamic lesson about your own heart in the face of death, to become your full self in the face of death, knowing just as you grasp it you're going to lose it all, is a very brave thing. And I think that's the triumph of Chris McCandless."