koreangrumblings:

-더라니 is yet another cause-effect grammar point.  It is used when in retrospect the result of a situation now seems obvious or predictable.

Imagine: after a huge dinner at a buffet, you wake up the next morning to a terrible stomachache.  You complain to your friend, but they are less than sympathetic.  They point out to you that, looking back on the previous night, you had stuffed your face, so your stomachache is the obvious result of that feast.  Your conversation in Korean might go something like this:

가: 오늘 아침에 배탈이 났어요.  I had a stomachache this morning.

나: 어제 뷔페에서 과식하더라니. (Looking back on it) You did overeat at the buffet yesterday.

Examples:

내가 너 시험 성적이 나쁠 줄 알았어. 공부 안 하고 계속 놀더라니. I knew your test score would be bad.  (Looking back on it) You didn’t study and just fooled around.

컴퓨터가 안 돼요. 고장 났나 봐요. 지난 주부터 이상하더라니. The computer isn’t working. It must be broken.  (Looking back on it) It’s been acting up since last week.

네가 감기에 걸리는 게 놀랄만한 일이 아니야. 이 추운 날씨에 얇은 옷을 입고 다니더라니.  You getting sick isn’t a surprise.  (Looking back on it) You kept going out in light clothes.

Coupled with 어쩐지, -더라니 carries with it a sense of belated realization.  It is used when you have received information that explains an already known fact. The closest English translation for this usage would be “No wonder”.

Example:

길에서 산 티셔츠가 한번 빨고 나서 줄어들더라고요. 어쩐지 값이 싸더라니.  The t-shirt I bought off the street shrank after just one wash.  No wonder it was cheap.  

마이틀 씨가 이번에 승진해서 보너스를 많이 받았대요.  어쩐지 그동안 기분이 좋아 보이더라니.  They say that Michael received a huge bonus with his promotion.  No wonder he’s been in a good mood lately.

그 학생의 부모님이 부자래요. 어쩐지 명품옷만 입었더라니.  They say that student’s parents are rich.  No wonder he wore only brand name clothes.