Since I've gone and ruined the moment, I change the subject to one of Gyllenhaal's favorite topics: meditation and spirituality. Gyllenhaal studied Eastern religion at Columbia University before dropping out to concentrate on acting, and he says he tries to meditate every day. "I hope I'm a spiritual person," he says. "I'm trying to be a spiritual person."

But how, I want to know, does he stay spiritually balanced? After all, he is literally a child of Hollywood—his father, Stephen Gyllenhaal, is a director (Losing Isaiah), and his mother, Naomi Foner, is a screenwriter (Running on Empty)—and he grew up surrounded by stars: Paul Newman taught him how to drive. Jamie Lee Curtis is his godmother. The road to keeping it real, he admits, has not been easy to find.

"I think even a few years ago I needed a lot more validation," he says. "I needed everyone to like me and think I'm great. But that attention doesn't work for me anymore. I realize that there's nothing at the end of that, so I can either use the validation to try to fill an insatiable hole or I can realize that this job is never going to do that. And yet I still love to act and I still love movies, so how do I approach this in the right way?"

He occasionally approaches it in an annoying way. During the filming of his biggest box-office hit to date, last year's $186 million blockbuster The Day After Tomorrow, the actor was difficult, he admits, often more concerned with being "really artsy" than with hitting his marks. Dennis Quaid, who played Gyllenhaal's father, sat him down and set him straight. "He's like, 'You gotta chill out, it's an action movie,'" Gyllenhaal recalls.

That stubborn streak of individuality can complicate relationships off-set as well. During the filming of Jarhead, Gyllenhaal and his costar Peter Sarsgaard, who happens to date Gyllenhaal's actress sister, Maggie, got into a bitter dispute over an incident neither will now discuss. But they eventually buried the hatchet and are good friends again. "He's completely into whatever he is doing in the present moment, and that draws people to him," says Sarsgaard. "But let me tell you, it can also be really annoying. Sometimes he's just too eager. Especially in the morning. We would be driving to the set, and he would be all revved up and play 'Candy Shop' five times in a row. I'm like, 'Can you please turn off that fucking song?'"

Not even Academy Award–winning directors can find the switch on Gyllenhaal. "I say this very lovingly, because Jake is wonderful and brilliant, but he can be a little bit of a pain in the ass," says Mendes. "If he gets a bee in his bonnet, he won't let it go. He'll just get blocked sometimes and basically gets stuck putting too much importance on one scene, or trying too hard with being absolutely brilliant. He's also the least technical actor I know. If I say to him, 'Lift the gun at the point when you turn,' he can't do it. He's not an actor who's designed to hit marks. So I just let him do his thing. And I'm not worried that he'll be hurt by what I just said. In a weird way, what turns him on is criticism." It's not easy being Jake, what with everyone want-ing you. But being wanted is boring. Being tested—well, now, that's something else altogether.