소 잃고 외양간 고친다 (So ilkko oeyanggan gochinda)

Literally: Fix the barn after losing the cow

Example: “도둑이 든 뒤에 경보기를 달다니, 소 잃고 외양간 고치는 격이다.” — Installing an alarm after the burglary is shutting the stable door after the horse has bolted.

English equivalent: Shut the stable door after the horse has bolted

Origin: Rooted in the genuine economics of traditional Korean farm life: an oeyanggan (cattle shed) was a simple wood-and-thatch structure, cheap and quick to repair — a single day's labor was generally enough to fix one that had fallen into disrepair. A cow, by sharp contrast, represented one of a farming family's single largest and most irreplaceable investments, since losing one to a collapsed, poorly maintained shed meant a real, often unrecoverable financial blow that no quick repair afterward could undo. Fixing the shed only after the cow was already gone captured, in one compact image, the particular folly of neglecting a genuinely cheap and easy repair until it caused a serious, permanent loss — the Korean idiom carries a harder edge than the loosely similar English "shutting the stable door after the horse has bolted," applying strictly to damage that's already become irreversible rather than to milder, more recoverable mistakes.