는단

The thing is, I'm telling you

Every line here uses it inside the frame 는단 말이다, which means the thing is or I am telling you. You reach for it to press a point the listener has not taken in, or to spell out the crux of what you are describing: the thing is, they are only open from nine to six; the thing is, Luke can really handle spice. It is a shortening of 는다는 말이다, literally the words are that. Polite versions end 말이죠 and 말이에요.

Register: conversational, emphatic