Sài Wēng loses his horse
Used to refer to situations where one has suffered a loss but actually ends up better off because of it; indicates that bad situations can become good ones
Positive
没有得到那份工作其实是塞翁失马，因为现在我已得到一个好得多的工作 | Méiyǒu dédào nà fèn gōngzuò qíshí shì sàiwēngshīmǎ, yīnwèi xiànzài wǒ yǐ dédào yīgè hǎo dé duō de gōngzuò
Not getting that job was actually a blessing in disguise, since I already got an even better job
[Source]
他丢了旧车，保险公司赔他一部新车，真可说是塞翁失马 | Tā diūle jiù chē, bǎoxiǎn gōngsī péi tā yī bù xīnchē, zhēn kě shuō shì sàiwēngshīmǎ
He lost his old car, but there was a silver lining: his insurance company compensated him with a new one
[Source]
A silver lining; every cloud has a silver lining
A blessing in disguise
北叟失马 (běi sǒu shī mǎ)
The 胡人 (hú rén) were people of northern or western ethnic groups in ancient China
《淮南子》(Huái Nán Zi), a piece written in the western Hàn (西汉, Xī Hàn) dynasty (206 BC - 8 AD)
During the Warring States period (475 - 221 BC), there lived a man called 塞翁 (Sài Wēng) who was good at fortune telling. One day, 塞翁's horse broke free and fled in the direction of the 胡人 (hú rén). His neighbors consoled him, but he simply said, "How do you know this is not a blessing?"
Several months later, the horse who had fled returned to 塞翁, bringing with it another horse. This time, everyone congratulated the man, but he replied, "How do you know this is not a source of disaster?" Later, his son, who liked to ride, was out riding the new horse when he fell and broke his leg. At this, the people consoled 塞翁, but he answered, "How do you know this is not a good thing?"
A year later, the 胡人 invaded, and all able-bodied men had to go out and fight. Of those who fought, many lost their lives, and those who didn't were severely wounded. 塞翁's son was the only one who was able to remain safe, precisely because he'd broken his leg falling from the horse.