Zhèyàng ēnjiāng-chóubào de xíngwéi lìng rén hánxīn.
Repaying kindness with betrayal like this leaves one heartbroken.
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Popularized by Wu Cheng'en's Ming-dynasty 《西游记》 (chapter 30), where the phrase is used when the Tang Monk fears that speaking out will cause a kidnapped princess to be killed by her captor - the archetypal ingrate scenario.