천고마비 (天高馬肥)

하늘은 높고 말은 살찐다 - In autumn, the sky is high and horses fat.

천고마비 (天高馬肥) is the Korean adaptation of the Chinese idiom ‘秋高马肥’. It describes the feel-good atmosphere of autumn - beautiful high blue sky and well-fed horses. However, this idiom does not always carry a positive vibe, it was originally meant to suggest something ominous.

During the Warring States Period, the Xiongnu, a federation of nomadic tribes, would infringe the northern border every autumn to raid and plunder the southern states on horseback. The 'horse' in the idiom refers to the horses bred by the Xiongnu. When their horses became 'fat' or strong during autumn, it signified that invasion of the south was imminent. Perhaps that explains why another idiom exists: 다사지추 (多事之秋). It can be literally translated as an autumn with many happenings; it means a period in time when many problems and issues erupt. 

If autumn was peaceful, the idiom passed down would have been 천고우비 (天高牛肥) or 천고양비 (天高羊肥).

천고양비 (天高羊肥)