sleep on brushwood and taste gall（卧薪尝胆）
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. fu was determined to revenge. he drilled his army rigidly until it was a perfect fighting force. three years later, he led his army against the state of yue and caught its king gou jian. fu took him to the state of wu.
in order to avenge his father's death, fu let him live in a shabby stone house by his father's tomb and ordered him to raise horses for him. gou pretended to be loyal to fu but he never forgot his humiliation. many years later, he was set free. gou secretly accumulated a military force after he went back to his own state. in order to make himself tougher he slept on firewood and ate a gall-bladder before having dinner and going to bed every night. at the same time he administered his state carefully, developing agriculture and educating the people. after a few years, his country became strong. then gou seized a favorable opportunity to wipe off the state of wu.
later, people use it to describe one who endures self-imposed hardships to strengthen one's resolve to realize one's ambition.
译文：
春秋时期，吴国和越国之间进行了一场战争，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，他严格的操练他的士兵，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，还每天在吃饭睡觉前尝一尝苦胆。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，然后，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。