During the Spring and Autumn period (770－476BC), the State of Wu launched an attack against the State of Yue. The King of Wu was seriously wounded and soon died. His son Fu Chai became the new king. Determined to avenge his father's death, Fu drilled his army rigidly until it became a perfect fighting force. Three years later, he led his army against the State of Yue and captured its king, Gou Jian. Fu took him back to the State of Wu.
Fu required Gou to live in a shabby stone house by his father's tomb and ordered Gou to raise horses for him. Gou pretended to be loyal to Fu, but his mind was filled with revenge. Several years later, he was set free. Going back to his state, Gou secretly accumulated a military force. To make himself tougher, he slept on firewood and tried a gall-bladder before having dinner and going to bed. At the same time, he developed agriculture, strengthened education and administered his state wholeheartedly. His country became strong within a few years. Then Gou seized a favorable opportunity to wipe off the State of Wu.
Later, people use the phrase to describe one who endures self-imposed hardships to strengthen his resolve to achieve his ambition.
wò xīn cháng dăn
xìng gāo căi liè
with great joy; in high spirits; in great delight; jubilant