"亏心事" refers that something goes against one's conscience. This sayingliterally means one won't be afraid of ghost's knocking at his door at night without doing anything against his conscience. It means that a quiet conscience sleeps in thunder. It also is written as "不做亏心事,不怕鬼叫门"。
例句
1、甲:听说警察明天要找你问那件案子。 Jiǎ: Tīngshuō jǐngchā míngtiān yào zhǎo nǐ wèn nàjiàn ànzi. A: It's said that the police would ask you about that case.
乙:我不做亏心事,不怕鬼敲门。他们要问就问吧。 Yǐ: Wǒ bú zuò kuīxīnshì, bú pà guǐ qiāo mén. Tāmen yào wèn jiù wèn ba. B: A quiet conscience sleeps in thunder. Go ahead.
2、甲:他现在出国,一定有什么问题。 Jiǎ: Tā xiànzài chūguó, yídìng yǒu shénmen wèntí. A: It's suspicious that he goes abroad right now.
乙:对,不做亏心事,不怕鬼敲门。他就是想要躲开那件丑闻。 Yǐ: Duì, bú zuò kuīxīn shì, bú pà guǐ qiāo mén. Tā jiùshì yào duǒkāi nà jiàn chǒuwén. B: I agree. A quiet conscience sleeps in thunder. He just wants to avoid that scandal.