To mark Youth Day, which fell on May 4, Sun offered one piece of advice, which carries some hard-won wisdom, to aspiring young athletes: "The future matters less than your commitment to the path you choose. Stay steadfast, and success will follow."

Born and raised in Yichang, Hubei province, Sun Jiajun grew up under the care of his grandmother.

In 2006, when he was just six years old, his grandmother first sent him to a summer camp where he was introduced to swimming. He was soon selected by a coach to join the city's sports school for systematic training. In 2013, Sun was chosen to join the Hubei Provincial Swimming Team.

Zheng Shan, his coach at the time, recalled: "When Sun first joined my training group at about 12 years old, he was very mature for his age and exceptionally hardworking. His greatest qualities were his passion for both swimming and life, and his unwavering dedication once he set a goal. He never cut corners in training — in fact, he often asked to increase the intensity and workload."

Five years later, Sun earned his place on the national team.

When asked about life outside the pool, Sun shared his love for movies — especially suspense and detective films. He dreams of coastal getaways, mentioning Sanya in Hainan province as a perfect retreat.