When writer/director Mike Mills was in his early 30s he had already directed a few short films and some music videos. But when his mother died, he began searching for material that might have deeper meaning – a quest that ultimately led to his six-year odyssey of bringing Thumbsucker to the screen.

"My mom got sick and died, and that brought on a period of reflection in my life. What I wanted to do was to make a film that might have real meaning for people," says Mills. Little did he know how difficult it would be to bring such a meaningful story to life.

"At first, investors said that none of the characters in the story clicked with them. I was getting nowhere, just going into people’s offices and coming up with nothing. But at the same time, the script was going around to various well-known actors, and when the cast was assembled, that was when I could raise the money. I spent almost all of my 30s making this film."

A hit at the 2005 Sundance Festival, Thumbsucker (based on the novel by Walter Kirn) tells the story of Justin Cobb (Lou Pucci), a depressed high school senior still addicted to sucking his thumb. His father, Mike (Vincent D’Onofrio), is distant and has no advice for him; his mother Audrey (Tilda Swinton) is more alert to his needs, but has few ideas on how he should better conduct his life. He is doing poorly in school, especially on the debate team, where Mr. Geary (Vince Vaughn), a teacher who is having a perpetual bad hair day, insists that Justin be more assertive. His lack of assertion interferes with his making any progress with his classmate Rebecca (Kelly Garner), a pretty but moody girl obsessed with environmental politics. Finally, his hippie orthodontist Dr. Lyman (Keanu Reeves) hypnotizes him to break his thumb-sucking habit, catapulting him into awful withdrawal.

Things are going nowhere fast for Justin, until he is put on Ritalin, which makes him a hyper super-achiever, a champion on the debate team, Rebecca’s lover and confrontational with his parents. How these threads are resolved takes up the second half of the film, which Mills says is really about "deeply flawed people who want to be anything other than themselves. They want to be ‘normal,’ but they learn that normal doesn’t exist," he says. "There are no magic ways for them to fix themselves. They realize that their flaws are what make them human and lovable."

Chosen from over 250 teen actors, Pucci was given the lead role because Mills saw that he didn't carry a false swagger like the other teens who auditioned. "He was really nervous and vulnerable, he didn’t try to hide that, and that’s what made me think of him as Justin," says Mills.

Pucci, whose look recalls a younger and more sensitive Johnny Depp, laughs when asked about his research into thumb-sucking adults. "I spoke to them – they have these groups where they get together and talk, and also there’s a Web site," says Pucci. "You can find it if you Google 'adult thumb suckers.' Basically they are no different than anybody else, and they don’t feel embarrassed about their habit. It’s a coping mechanism, like smoking a cigarette. And I can relate to that, because for me, acting and putting on the mask of a character is my coping mechanism."

Pucci has the greatest respect for Mills, whose direction included two weeks of improvisational rehearsals. "We didn’t do the script. Instead, we talked about our pasts and how we’d gotten where we are as a family. Mike even gave Tilda and me a $100 and we went to the mall together and shopped, to get closer to each other. But with Vincent D’Onofrio, he kept us a little apart, which created the distance that we have playing father and son."

Pucci now lists D’Onofrio as one of his favorite actors. "He has incredible ways of getting into a character, like keeping his nails trimmed to a certain length so he gets a certain feeling in his fingers that he associates with the character. He gets so absorbed, it’s amazing."

Near the end of the film we finally find Justin Cobb running happily down a busy New York street, apparently headed fast toward the fulfillment of his aspirations. A happy ending? No, says Mills. "Justin’s happy at the moment, but there are more tough times ahead. You know, I was going to make him stumble and have a pratfall during that run, but I thought I’d give him that happy moment, after all he’d been through."

Thumbsucker releases in theaters Sept. 16.