귀가 얇다.

The idiom '귀가 얇다' (gwi-ga yalda) literally translates to 'ears are thin.' This vivid imagery suggests that one's ears are so thin that words or sounds can easily pass through them and influence the person, implying a lack of discernment or resistance to external persuasion. The expression is thought to have originated from a traditional understanding of how people perceive and process information. In Korean culture, the ear (귀, gwi) is often metaphorically associated with one's capacity for listening, understanding, and being influenced. When someone is described as having 'thin ears,' it means they readily accept what they hear without much critical evaluation. This can be contrasted with someone having 'thick ears,' which would imply an inability to hear or a stubborn resistance to advice, though this specific counter-idiom is not as commonly used. The concept of being easily influenced or gullible has been present in various forms in Korean society for centuries, reflecting a value placed on independent thought and sound judgment. The idiom likely solidified its current form and usage as a concise and evocative way to describe this personality trait, becoming a common part of everyday Korean discourse to comment on someone's susceptibility to others' opinions or schemes. It is a widely understood and frequently used idiom in modern Korean.