형설지공이 · 형설지공을
success through diligent study despite hardship
Example
그는 형설지공으로 공부해서 의사가 되었어요.
He studied hard against all odds and became a doctor.
Word parts
형 firefly+설 snow+지 of+공 merit
Literally 'achievement by firefly light and snow glow' — poor scholars reading at night.