臥薪嘗膽 [卧－尝胆]

Jyutping ngo6 san1 soeng4 daam2
Pinyin wò xīn cháng dǎn

Definitions (CC-CEDICT)
  1. lit. to sleep on brushwood and taste gall (like King Gou Jian of Yue 勾踐|勾践[Gou1 Jian4]), in order to recall one's humiliations) (idiom)
  2. fig. to maintain one's resolve for revenge
Definitions (CC-CANTO)
  1. endure hardship to accomplish an ambition
Definitions (Wiktionary)
  1. phrase, idiomatic
    to undergo self-imposed hardships; to nurse vengeance; to endure hardships to accomplish some ambition