And heartbreaking finality.
When Penn - an actor and director unafraid to put his views out there, whether about Katrina or Iraq - got hold of Jon Krakauer's book Into the Wild, he was rocked to his core.
"From the time I read the book, shortly after it came out in '96, I knew I wanted to make this movie," he says, dressed in natty black and camped in a hotel room on the afternoon that Into the Wild - which stars Emile Hirsch as McCandless - premiered at the Toronto International Film Festival.
"I tried for a long time. It took a long time for the parents to feel comfortable with the idea of a movie being made," Penn says.
But over meetings with Krakauer, and Walter and Billie McCandless, Penn made his case, gaining the father and mother's trust. Once he had their blessing, he set to work writing the screenplay - he didn't need to reread the book, he knew it that well. And then he set out on his own cross-country journey ("due diligence" he calls it), retracing McCandless' route - stopping at the same South Dakota farm, the same Oregon beach, talking with some of the same folks McCandless spent time with.
In the end, Penn found himself in the remotest precincts of the 49th state, having crossed three rivers, the Savage, the Sushana and the Teklanika, to arrive at the rusted bus that McCandless had made into his home.
"There were moments of sad reflection along the way," Penn says. "I wanted him to be there so I could ask him something. But I've lived with this story and [with] my response to Jon Krakauer's book 10 years before I started this project, and I came to realize that I'd been writing it in my head the whole time. . . .
"And the movie is the book to me. When you see the movie, that's what I read. In that sense, I was just a faithful adapter."
