卧薪尝胆臥薪嘗膽

wò xīn cháng dǎn

ㄨㄛˋ ㄒㄧㄣㄔㄤˊ ㄉㄢˇ

Idiom

1(fig.) to maintain one's resolve for revenge

2(lit.) to sleep on brushwood and taste gall (like King Goujian of Yue 勾践|勾践, in order to recall one's humiliations) (idiom)