苦 心

painstaking effort
to take a lot of trouble
laborious at pains

Appears in

苦心经营kǔ xīn jīng yíngto build up an enterprise through painstaking efforts 煞费苦心shà fèi kǔ xīnto take a lot of trouble (idiom); painstaking 苦心孤诣kǔ xīn gū yìto make painstaking efforts (idiom); after much trouble 皇天不负苦心人huáng tiān bù fù kǔ xīn rénHeaven will not disappoint the person who tries (idiom). If you try hard, you're bound to succeed eventually.