Schultz tells Billboard that Mockingjay director Francis Lawrence explained to him that the song -- sung by Lawrence's character Katniss Everdeen in the film -- had "to be something that can be hummed or sung by one person [or] by a thousand people" and that it couldn't be "overly complicated." Schultz adds that "it's supposed to almost feel like a nursery rhyme ... innocent, even though it has a really dark undertone to it."
Armed with Lawrence's instructions and Collins' lyrics (as originally written in Mockingjay), Schultz and Fraites swiftly submitted a "couple melodies in about a day and a half or two days" in September of 2013.
"Eventually, they (the Mockingjay film executives) said 'this one seems promising, let's do this,'" says Schultz.
Still, the pair weren't sure their tune would be used, considering it's "such a big movie" and they assumed there were "probably a lot of people trying to write a melody."
"I just don't think we really had our hopes up."
Their lack of confidence was unwarranted, as the director featured the song in a pivotal Mockingjay scene that proves Everdeen can be the face of the rebellion. The song's use in the film clearly moved audiences, as it debuted at No. 12 on the Billboard Hot 100 the week of its release, powered by 200,000 first-week downloads (according to Nielsen Music). It has sold 1.1 million to date.
"The first time that I heard it was going to be (officially in the film) was through Francis Lawrence," Schultz says. "He texted us and said 'It worked out great in the movie. We just shot the scene. Jen was really nervous but it went great.'"
And what about Jennifer Lawrence's much-publicized dislike of her singing voice? (She told David Letterman in 2014 that singing in front of people was her biggest fear and that she cried on set the day the scene was filmed.)
"I thought she did a great job," says Schultz. "If she's not sure of herself, that doesn't really come through in the performance. I think it sounds really natural and vulnerable, and I really like that.
"She has this rawness quality to her voice that I love about a lot of singers that I identify with."