가: 컴퓨터가 30%나 세일을 하네요,
Computers are a surprising 30% off.
나: 진짜요? 이렇게 세일할 줄 알았으면 조금만 기다릴걸 그랬어요. 지난주에 샀거든요.
Really? If I had known they were having such a big sale, I would have waited a bit longer. I bought one last week.
This expression is used when the speaker wants to express regret or a feeling of lament about something he or she should have done, or did but should not have done. When referring to something that should have been done but was not, -(으)ㄹ걸 그랬다 is used, and when referring to something that was done, but in hindsight should not have been done, either -지 말걸 그랬다 or 안 -(으)ㄹ걸 그랬다 is used.
• 오늘 학교 축계에 안 갔는데 유명한 연예인들이 왔다고 해요. 축제에 갈걸 그랬어요.
Today, I didn’t go to the school festival, but I heard that a lot of famous stars attended. I should have gone to the festival
• 시험이 너무 어려워서 시험을 망쳤어요. 이렇게 시험이 어려울 줄 알았으면 공부를 더 많이 할걸 그랬어요.
The test was so difficult that I failed it. If I’d known it would be so difficult, I would have studied more.
• 오늘 친구랑 놀러 갔는데 갑자기 비가 왔어요. 오늘 가지 말걸 그랬어요.
I went out with my friend today, but it suddenly started raining, I shouldn’t have gone out today.
This word 그랬다 in this expression can be shortened to simply -(으)ㄹ걸. This is an Informal form of the expression used only with those with whom the speaker is close or when talking to oneself.
가: 우리 과 친구들이 여행 간다는데 너도 같이 갈래?
나: 나도 가고 싶은데 돈이 없어. 이럴 줄 알았으면 돈을 좀 아껴 쓸걸.
The expression -(으)ㄹ걸 can also be used to express a supposition. However, this suppositional -(으)ㄹ걸 is spoken with a rising intonation and is only used in informal speech.
(See Chapter: ‘을걸요 Expressing Conjecture and Supposition’ here).
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