Literature Reference: 古人无宿诺，兹道以为难。——《东平留赠狄司马》 The ancients had no promises left unfulfilled, such a principle is considered difficult. Source from 'Dongping Liu Zeng Di Sima'.
宿: Celestial Mansions.
诺: Promise, pledge. Metaphorically signifies honesty and trustworthiness.
Meaning: To keep one's promise, never breaking it, embodies the qualities of integrity and steadfastness.