Who is the good child?

Debate Topic: When fulfilling a promise, are the motivation and process more important than the final outcome? Scenario: Late summer breezes rustled through the eaves of an old house. Standing at the doorway, a mother adjusted the collars of her four children, who were about to embark on a journey. As they parted, she whispered, "When you're out in the world, remember to write back and let me know you're all doing well." The four children nodded, solemnly promising their mother. However, the four letters sent during their travels met vastly different fates. The eldest son, Cheng An, handed his completed letter to a hotel attendant to mail, but the attendant forgot. The second daughter, Nian Qing, mailed it herself, but it was returned due to her carelessness in filling out the wrong address. The third son, Jing Yun, completed every step perfectly, but his letter was unfortunately lost in the postal system during a storm. The youngest daughter, Si Yu, after correctly mailing her letter, even called to confirm, but none of them arrived. So, she read the contents of the letter aloud over the phone. Question: Who truly kept their promise to their mother?