to put in a lot of effort but get no thanks; to work hard but receive no appreciation; thankless effort
他主动帮助同事解决了一个技术难题，结果反而被指责没有事先沟通，真是费力不讨好。
He proactively helped a colleague solve a technical problem, but was instead blamed for not communicating beforehand. It was truly a thankless effort.
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