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
卧薪尝胆
春秋时期，吴国派兵攻打越国，吴王不幸受了重伤，不久就死了。他的儿子夫差作了吴国的新国王，他发誓要替父亲报仇。于是，他严格操练他的士兵，把他们训练成了一支非常厉害的军队。三年以后，他对越国发动了战争，抓住了越王勾践，把他带回了吴国。
为了复仇，夫差让勾践住在他父亲墓旁的破石屋里天天看墓、喂马。勾践表面上服从，心里面却想着复仇。几年以后，勾践被放回越国。他立刻开始秘密聚集一支军队。为了提醒自己不要忘了报仇，他睡在柴上，每天吃饭睡觉前还要尝一尝苦胆。同时，他专心治理国家，大力发展农业，加强民众教育。几年后，越国又变得强大起来，于是勾践抓住一个适当的机会消灭了吴国。
后来，人们用它来形容人刻苦自励以达到自己定下的目标。
xìng gāo căi liè
兴高采烈
with great joy; in high spirits; in great delight; jubilant
