During the Warring States period, Wu Zixu's family was tragically executed by King Ping of Chu due to the slander of Fei Wuji.

Wu Zixu fled to the State of Wu and later assisted King Helü of Wu in conquering the State of Chu. Out of deep hatred, Wu Zixu exhumed King Ping of Chu's corpse and flogged it 300 times.

His friend, Shen Baoxu, who remained loyal to Chu, sent a letter to Wu Zixu criticizing his actions. In the letter, Shen Baoxu wrote, '吾闻之，人众者胜天，天定亦能破人。' (I have heard that a multitude of people can conquer heaven, but heaven's decree can also break man.)

Although Shen Baoxu's original intention was to convey that even human power has its limits against fate, the first part of his statement '人众者胜天' evolved into the idiom '人定胜天', emphasizing humanity's ability to overcome natural forces or destiny through determination and effort.