After graduating from the Faculty of Journalism and Communication of the University of Social Sciences and Humanities, Vietnam National University Hanoi, Ha Le Diem registered for a documentary filmmaking course at the Centre for Assistance and Development of Movie Talents. Diem's initial purpose was just to satisfy her curiosity. But she immediately became fascinated with the genre.

Diem's first short documentary film was titled "I go to school". In 20 minutes, it tells the story of a woman who was infected with HIV by her husband and still has to take care of her son alone while struggling with the “disease of the century”. The film was praised for its delicate visual storytelling. Diem’s feminine thoughts are revealed naturally to the lenses.

Diem recalls how she made the film, “One time when I came to the woman's house, I realized that she was very worried for me. I really felt at ease.

“One afternoon I crossed the stream near her house. Suddenly the hydroelectric dam released water and I got wet. It was winter and very cold. She felt sorry for me and said she would give me her trousers. Then she stopped and asked me not to use her trousers because she was worried I might get infected. During the meal time, she sat far from me. That showed me that she is very careful about protecting other people around her,” Diem said.

“I go to school” won the Silver Kite award in the Short Film category at the Vietnam Cinema Association Awards in 2013.

Clearing the distance with the characters, the most difficult step for documentary filmmakers, made Diem's success.

She gained the character’s trust who later became willing to tell her story in front of the camera objectively and honestly. Diem was able to do it naturally. Perhaps it was her sincerity, clear voice, and warm smile that brought her closer to her character.

In 2017, she went to Sapa and lived with the family of Di, the character in her documentary "Children of the Mist".

Di's father told Diem that the first time he picked her up at the Sapa bus station, he was surprised to see her carrying a lot of things - a large bag of clothes and a backpack full of cameras and film equipment. He drove me straight to the fields, because it was sowing time and no one was at home.

“When I got there, I went down into the fields like everyone else. When everyone went home for lunch, I followed them. Di's father said he thought I could ‘survive’ there as a Mong person. That made him feel secure and let me stay in his home, go out with Di, and work in the fields like anyone else,” said Diem.

The idea of making a movie about Di's childhood came while Diem was filming Di and her children playing together, which, Diem said, reminded her of herself and her friends many years ago when Diem and her friends had fun and happy moments.

After more than two years of filming, Diem considered Di's family her own, and Di's neighbors, teachers, and friends are close to her own life.

Diem recalled when she was filming Di, she slept at Di's house. When she was filming others, she stayed in their house for a few days before returning to Di's house.

“Di's mother once said ‘when you finish your work, come back home’. Hearing the phrase ‘come back home’ moved me deeply because only family members talk to each other like that. If they considered me a guest, they would say ‘come back to our house’,” Diem said.

The story took shape over 3 years, from the initial idea to the final footage. Gradually, 100 hours of film were edited down to a 90-minute film.

Vy Nguyen Anh Phong, another young filmmaker, helped Diem prepare documents to solicit financial support from film festivals and film funds around the world.

Phong said Diem did most of the filmmaking by herself. As friends and colleagues, we often talked and gave each other advice and suggestions.

"Sometimes we felt the film was stuck and couldn’t go any further. But the film was eventually completed and gave us an experience beyond anything filmmakers like us had ever imagined. The result was worth every hardship Diem has gone through,” according to Phong.

The process of making "Children of the Mist" was also a process of maturation for Diem. The film unlocked opportunities to go to new places around the world, meet lots of well-known people in the film industry, and learn many valuable lessons.