The heartwarming story behind the 'Wonder' moment that made director Stephen Chbosky cry

Heading into its third weekend nestled comfortably among the top box-office grossers, Lionsgate’s surprise hit Wonder proves that moviegoers are never too old — or too young — for a good tearjerker. And viewers are freely fessing up about tearing up on Twitter, where even acclaimed novelist John Green — who has some experience making other people cry as the author of The Fault in Our Stars — has credited Wonder for making him all verklempt.

Like the best tearjerkers, Wonder­ — which follows a year in the life of the Pullman family, whose youngest member, Auggie (Jacob Tremblay), has a rare facial deformity — earns its tears honestly, with low-key but unabashedly emotional storytelling that makes room for multiple cry points. I’ve seen the film twice now, and each time the sequence that gets me is a performance of Our Town starring Auggie’s older sister, Via (Izabela Vidovic). Technically, Via’s estranged friend Miranda (Danielle Rose Russell) is the star of that high school production, but at the last minute Miranda fakes an illness so that understudy Via can step into the spotlight in the pivotal role of Emily while her parents, Isabel and Nate (Julia Roberts and Owen Wilson), watch. Besides reminding me of my own theater nerd days (not to mention my absolute favorite episode of The Wonder Years), the scene really loosens the proverbial dam when Via delivers Emily’s beautiful beyond-the-grave monologue, as Isabel’s own memories drift back to her daughter’s fourth birthday party. Thornton Wilder’s words plus a visual reminder of the fleetingness of childhood while sitting in the theater next to my own 10-year-old? Forget it — instant waterworks.

As it turns out, the Our Town sequence is Wonder director Stephen Chbosky’s main cry point as well. “I just love the themes of it — of appreciating what you have and embracing life,” he told Yahoo Entertainment in a recent interview, adding that the play was his high school’s senior-year production. “I couldn’t think of a better way to illustrate that than by having Isabel realize that the last 10 years of her daughter’s life had just vanished for her because she was so focused on Auggie. I’ve been moved by how many mothers have come up to me, after seeing the movie, and singled out that moment as a favorite of theirs.”

Chbosky went on to reveal that he has his own highly personal reasons for tearing up when Via delivers the closing monologue: That’s his daughter who plays the young Via in Isabel’s flashback. “It’s very personal,” he says, getting audibly emotional while explaining that the cameo came about because shooting commitments kept him from attending her fourth birthday party. “That was heartbreaking for me. When they came to visit me in Vancouver [where Wonder was shot], I was able to stage the birthday that I missed. So I’ll always cry at that point, because I get to say I’ve never missed one of my daughter’s birthdays.”

Per Chbosky’s memories, it sounds as if his daughter’s day on set was more of a gift for him than it was for her or, for that matter, her famous scene partner. “Julia joked, ‘I’ve never been your second-favorite actor on set before, and I don’t know if I like it,'” the director says of watching the Erin Brokovich star play mom to his little girl. “And it was true! Here’s this international icon, and all I’m doing is looking at my kid saying, ‘You’re so good! You’re doing so well.'” At the time, his daughter wasn’t phased by all the attention or having to deliver her one line: “I wish for a baby brother.” In fact, she didn’t even remember shooting the scene when she saw the completed film recently. “She’s 5 now, and I brought her to the premiere. She kind of remembered all the men and the lights, but she didn’t know who Julia Roberts was. She sat through the whole movie and wants to see it again. I thought, ‘Wow, if we’ve got the 5-year-olds, we’ve got something.”

As the box office has borne out, Wonder‘s appeal really does span age demographics, from 5 to 85. That makes it an increasing rarity on the Hollywood landscape: a live-action, PG-rated film that parents can enjoy as much as, if not more than, their kids. It’s also a faithful translation of a beloved novel that avoids angering fans with sizable changes or annoying them by simply being a book-on-film. Chbosky is two for two in that regard; his first feature, 2012’s The Perks of Being a Wallflower, adapted from his own 1999 novel, was also praised for retaining what people loved about the book without slavishly re-creating every detail. Asked if there’s any particular secret behind a successful adaptation, the writer-director says he personally focuses a lot of attention on the casting process. “The author might have four chapters to introduce a character, but the filmmaker has five seconds, so the person had better be perfect for the part. Also, you’re always looking for the picture that’s worth a thousand words.” Like, say, the picture of a 4-year-old celebrating her birthday for a second time while her proud father looks on.

Wonder is playing in theaters now.

Read more from Yahoo Entertainment:

• How all those ‘Star Wars’ cameos wound up in surprise box-office hit ‘Wonder’

• ‘Wonder’ 101: Julia Roberts, Owen Wilson, and cast explain story behind new charming new movie