It's a good question! I sometimes wondered how English speakers would understand that!! I would make up some examples for you. 1. 나는 어제 너를 만나지 못해서 참 아쉬워. I wish I could've met you yesterday. 2. 다음 기회가 있겠지. 너무 아쉬워 하지 마. There will be another chance for you. Don't be so sad. 3. 아, 아깝다! 방금 지하철 탈 수 있었는데. Oh, it was so close! I could've caught the last subway. Anyway, 아깝다 sounds like "So close!" to me. I want to find the exact expression in English but can you tell me one??