One is unyielding when one has no private desire.
This idiom is based on Confucius' observation on Shen Cheng, one of his 72 major disciples. As recorded in Lun Yu (The Analects of Confucius), the Master (Confucius) said, "I have never met anyone who is truly unyielding." Someone replied that Shen Cheng was such a person. But the Master said, "He is driven by desires. How can he be unyielding?" This indicates that if one has too many desires, one cannot remain firm, upright and honest.
The idiom is about the importance of restraining oneself. It is particularly true with the officials. They will remain upright and fearless if they can resist temptations and inducements, remain selfless, and be free of irrational desires.
Addressing the meeting commemorating the 120th anniversary of the birth of Premier Zhou Enlai (1898-1976), held in March 2018, Xi Jinping quoted the Chinese saying: "The ocean is vast because it admits all rivers. The mountain peaks erect hundreds of feet high, because they are free from any worldly bond." He hailed the former premier as an outstanding role model who was strict with himself, led a simple life, and exercised lifelong dedication with no expectation of recompense. The premier had exhorted the leading officials to stand the tests of their conviction, political integrity, social connections, relatives and daily conduct, and observe the political norms and fine conduct of Chinese Communists.
无欲则刚
“无欲则刚” 出自《论语》中孔子对弟子的评价：“子曰：‘吾未见刚者。’或对曰：‘申枨。’子曰：‘枨也欲，焉得刚？’”人的欲望太盛，便难有坚定刚强之德，难以刚正不阿、正道直行。“欲”指各种私欲、贪欲；“刚”即刚正公道、正直有力。“无欲则刚” 是一种克己的功夫，讲的是立身处事尤其是执政做官的基本道理：一个人面对来自各方的种种诱惑，应该大公无私、端正品性、淡泊守志，不要有非分的贪图，这样就能一身正气，无所畏惧。
2018年3月，习近平在纪念周恩来同志诞辰120周年座谈会上指出，“海纳百川，有容乃大；壁立千仞，无欲则刚”。周恩来同志就是这样的人，他毕生严于律己、艰苦朴素，只求奉献、不思回报，并且告诫领导干部要过好思想关、政治关、社会关、亲属关、生活关，保持共产党人的政治操守和优良作风。