The conventional wisdom regarding Sean Penn's justly acclaimed rendering of Into the Wild is that the film is "faithful" to the Jon Krakauer book. This is utterly cracked, and the misconception is illustrative of my staunch "books are not movies" philosophy. Not only is Into the Wild not "faithful" to the book, but it couldn't possibly have been faithful and remain a narrative film. Sure, it dutifully replicates what Krakauer was able to discover about Chris McCandless' adventure – most of the supporting characters, destinations and events are here, and some lines of dialogue are lifted from Krakauer's account. If that's all it takes for a movie to be "faithful," then I guess it's faithful. But that ignores the fact that the book and the film were trying to accomplish fundamentally different things, and went about it in fundamentally different ways.

Krakauer's book – which, by the way, is a national treasure – is first journalistic, and then philosophical. The author did painstaking research to piece together the details of McCandless' journey and death from interviews, personal observations, and Chris's own writings. What emerged probably wasn't what Krakauer, who obviously sympathizes and identifies with his hero, would have preferred: the picture of McCandless his sources paint is that of a young man who is bright and curious, but also inconsiderate, arrogant, and often downright unpleasant. (The letter he wrote to "Ron Franz," Hal Holbrook's character in the film, haranguing the octogenarian to sell his possessions and go on the road, is painful to read.)

Much of what Krakauer presents is openly speculation and conjecture. We can't know, for example, whether or not McCandless actually had a major change of heart leading up to his death and felt ready to rejoin society, forgive old wrongs, and embrace family and friends -- but a few things Krakauer learned suggest that he may have. He doesn't know, and presents it as an interesting mystery, a possible clue to Chris's character.

Having presented the most complete possible account of McCandless' journey, Krakauer then sets about trying to understand him. To that end, he offers historical accounts of similar loners seeking epiphanies in the wilderness – like the famous story of Everett Ruess – as well as his own experience as an angry young mountain climber attempting an incredibly dangerous solo assault on the Devil's Thumb in Alaska. Whatever McCandless was, Krakauer suggests, he wasn't mad or completely inscrutable. Rather, he was brave enough to answer a call that a lot of people hear and ignore.

McCandless' story is similarly personal to Sean Penn, but Penn is interested in neither journalism nor, really, philosophy. His Into the Wild is neither a documentary nor a treatise; it's a character study. Some ambiguity remains, but a lot of the questions that Krakauer asks, Penn and his actors answer – Krakauer's doubts turn into emphatic assertions. Where the book was a searching inquiry, the movie is a skilled, insightful dramatization. A good film? Very much so. Faithful? Ha.

For example, Penn's obvious affection combined with Emile Hirsch's sharp eyes and easy smile immediately dismiss any notion – very prominent in the book -- that McCandless was actually kind of a jerk. Penn eliminates the suggestion in ways that are sometimes subtle: While Krakauer's version of McCandless and Ron Franz's goodbye has the boy brushing off the old man's poignant request to adopt him with a brusque "we'll talk about it after I get back from Alaska," his response in the film is a loving, profoundly moved "Ron, could we talk about this after I get back from Alaska? Would that be okay?" And Hirsch's McCandless was much more likely to respond to another character begging him to call his parents with a wide smile and a quote from Thoreau instead of the harsh "maybe I will and maybe I won't" we get in the book. Penn solves the enigma of who Chris McCandless was: he was a kind, good-hearted boy who, in his youthful drive and impertinence, made a tragic miscalculation that cost him his life. There's no room for the inconsiderate, aggressive, somewhat intimidating McCandless that Krakauer envisioned as a distinct possibility.

The "miscalculation" I alluded to is another element of this. To Penn, there's no question that McCandless underwent a conversion of sorts in his last days in Alaska. "Happiness only real when shared" isn't just a notation that Chris made in a book, but the soul of the film; that he signed one of his final notes with his real name isn't just a desperation move, as Krakauer admits it may well have been, but evidence of a fundamental change of heart. To Penn, McCandless' earlier statement that "you're wrong if you think happiness is derived principally from human relationships" is his fatal mistake, and his "deathbed" realization of how wrong, rash, and stupid he had been is his great tragedy. His last moments on earth consist of a light shining down from heaven as he forgives his family and, in his mind's eye, runs into their arms. There's nothing ambiguous about it. This is the story Sean Penn wanted to tell.

It is not, crucially, the story Krakauer wanted to tell (though a couple of these may have been possibilities he wanted to raise), and this is why the notion of Into the Wild being faithful to its source is so absurd. I want to be clear that I mean none of this as an aspersion on the film. I think it's fantastic, and what Penn does with McCandless' story is heartbreaking – in some ways more so than the book. What Penn realized is that while the book is an outstanding work of investigative non-fiction, it wasn't a story, or at least not one that would have worked on the screen. So he took what was a circumspect, thought-provoking work of journalism and turned it into a bold, dramatic American tragedy. It was one of the best films of last year. But it was "faithful" to the Krakauer book in only the most superficial ways.