In all of Wicked, one moment rises above all the rest. It’s the finale of Act One when the would-be Wicked Witch Elphaba finally embraces her powers and decides to fly, changing not just her life, but the lives of everyone in Oz. And she does it by singing the song “Defying Gravity.”

Much like the stage show, director Jon M. Chu uses “Defying Gravity” as the finale to his Part One of Wicked, now in theaters.. Unlike the stage show though, audiences won’t see Part Two in 20 minutes. It’ll be a year. So Chu had to be extra careful with the song so that it was everything fans of the show had been waiting years to see, carried the same emotions for people watching the movie for the first time, but also wrapped up the story in a way to leave audiences satisfied for a year. “It was hell on Earth,” Chu told io9 about finding that balance.

Bringing “Defying Gravity” to the screen is something  Chu was thinking about long before he signed on to direct the Wicked movie. Chu saw the show in early 2003, months before it came to Broadway, and instantly began imagining what it would be like as a movie. And, in fact, he keyed into one moment in particular. You guessed it.

“‘Defying Gravity,’” Chu told io9 when asked what he wanted to adapt the most. “That’s the easy one to go to. But it’s way more difficult than I thought. Because the power of those words, the brilliance of [songwriter] Steven Schwartz is in the specificity of those lyrics. You have to be right there with her and yet you want the scope of the flight and you want to experience it. So picking where we were big and where we were with her, that was torture actually. I had many versions of how to do that. But when we leaned into where we needed to be emotionally with her, that’s where it really took flight, no pun intended.”

Chu then dove a bit deeper into the specifics of the scene. Where he chose to expand, where he chose to add things not from the musical, and more. Here’s what he said when asked about living up to the hype of the song but also making sure it fit in this movie.

“That was scary,” Chu said. “When you split the movie into two, you have to have that first movie feel like a complete movie. So there’s a lot of work, [a lot of] plumbing that had to be done beforehand. ‘The Wizard and I,’ how that had to be the antithesis to [‘Defying Gravity’]. You go from the lowest ground, up to the highest ground, onto that edge, and she’s not quite ready to be with the bluebirds that fly over the rainbow… but she’s going to.”

“And how do you see her as a kid so you can root for her in all of these moments? And, in ‘Defying Gravity’ specifically, this is a breakup of these two people we fall in love with. Who had such a moment at the OzDust. And so the moment she says, ‘Come with me, are you coming?’ The unsaid thing is ‘I’m not coming. I want what you want but I found my destiny.’ To me, those were so powerful, and those girls understood it so intrinsically because [Ariana Grande] was living Galinda, [Cynthia Erivo] was living Elphaba. They are so different from each other, but they share this beautiful humanity together. And so that was really hard.”

“The moment that she’s supposed to just say, ‘It’s me,’ and she flies up, you’re waiting for that. But I love the fact that she didn’t earn it, actually. We needed her to feel that her purpose was right, not just for anger, not because she’s been dismayed, but why? So her falling out the window and seeing her younger self, to me, was the real reason she flew. She had to save herself for that little girl in herself. And so I loved that. And those were all very difficult versions. We did versions without it. We did versions with it. But in the creation of it, I knew that it had to do so much more than just be an end song. It had to tell the end of the story and conclude what the other characters were and give us what it felt like to watch ‘Defying Gravity’ on stage. So all those things factored into that. It was hell on Earth.”

Adding to those struggles was the fact that production had held filming of “Defying Gravity” until later in the shoot and then, due to the writer’s and actor’s strikes, had to postpone it. It wasn’t until after the long break that everyone came back to do the movie’s biggest number.

“We had to come back to do ‘Defying Gravity’ which was emotionally difficult for Cynthia and Ari,” Chu said. [Cynthia] had trained a year to do those stunts. And to know where to put her voice. And suddenly for six months she’s not doing it and she has to come back. For us, it actually really helped in the end because we got to gather our energy again. We had been shooting for 160 days at that point. And I think she dropped in so quickly and easily. And Ari also dropped in really easily. They were these characters and it was not as difficult as I thought it would be.”

The result speaks for itself. The song gives the film a solid ending with Elphaba embracing her powers and Galinda choosing her path; it also incorporates footage of everyone else and has all the excitement to end things on a high note. The story will then continue next year and, while it’s not quite “Defying Gravity,” Part Two does have a similarly epic song: “For Good.”

Wicked Part One is now in theaters.

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