Tough Out follows a group of "children in dilemmas" who pursue their dreams on baseball fields. [Photo provided to China Daily]

That emotional resonance explains Sun's persistence.

Many difficult moments are captured by director Xu Huijing in Tough Out. For example, in the search for a suitable location, Sun's team had to constantly relocate from one place to another around Beijing.

When they finally find an alternative facility, after the previous one is slated for demolition, the nearby elementary school is set to close down, meaning that there's nowhere to fulfill the educational needs of the children.

However, compared with the physical challenges, such as locations and equipment, remedying the psychological plight of the children often seems an even more insurmountable challenge.

Filming began in 2016 and one boy's melancholic demeanor immediately attracted Xu's lens. The boy, named Xiaoshuang, is from the countryside of Baoding, Hebei province. Living with his uncle in tough conditions, he never sees his parents. The sentimental Xiaoshuang became an unintended protagonist in the documentary.

Following his story, Xu gradually steps into the world of the children. With a childhood spent in rural surroundings, much of the director's work has found its focus on the countryside.

"I met a bottleneck in documentary production by then," Xu says. "But the children made me realize that a documentary doesn't just have to passively portray the social issues in the countryside. We can also explore the actions that can be taken to solve them."