Tiáojiě fūqī chǎojià shì chī lì bù tǎo hǎo de shì, shǎo guǎn wéi miào.
Mediating a couple's fight is a thankless task — better stay out of it.
Tips
history
Recorded in Wu Jianren's 《二十年目睹之怪现状》 (late Qing novel): the narrator complains that spending money this way is 吃力不讨好. The phrase already had its modern colloquial sense by then.
grammar
Five characters, not the usual four — but treated as a chengyu. Often used predicatively: 这事吃力不讨好 (this job is thankless). Can also modify a noun with 的: 吃力不讨好的工作.
