At fifty-five, Zhang Qingsong has spent his life working tirelessly. For years, he has carried fifty-kilogram bags of cement at construction sites, leaving his shoulders covered in thick bone spurs. Thirty-three years ago, his mother fell gravely ill and urgently needed 3,000 yuan for surgery. Their impoverished family could not afford it, so his mother chose to give up treatment, determined to save the money for her son's education. On the day she passed away, she told him to come home early after school because she would steam sweet potatoes for him. But young Qingsong stayed out playing soccer and returned late, only to find an empty earthen bed and half a cold sweet potato on the stove. That moment became a lifelong regret that haunted him. In the years that followed, he shouldered the family's burdens alone, working to support his family, getting married and raising a daughter, silently swallowing every hardship and grievance while keeping one word buried deep in his heart, a word he never dared say to anyone else: "Mom."