Because of how it sounds, "yako-jukda" is often mistaken for a Japanese borrowing, but it is genuinely native Korean. The key lies in the word yako. Around the Enlightenment era, Westerners' noses struck Korean eyes as unusually large and high, so people called them yangko-baegi — "big-nose folk." From this yangko ("Western nose"), the initial sound dropped away to leave yako, which gradually became slang for one's nose-bridge, or "pride." And the bridge of the nose stands for a person's self-regard and high spirit. For that nose-bridge to "die" is for one's spirit to be broken and deflated. So "yako-jukda" became a colloquial way of saying "to lose heart," and "yako-jugida" a way of saying "to break someone else's spirit."