~(으)니까: It is used to represent an action and a coresponding consequence. Usually, the action is the reason of the consequence apparently, but sometimes the speaker is not sure about the actual reason. For example, ex) 잡으니까 도망갔다. I caught it, and it ran away. (but the speaker is not sure whether it ran away because I caught it) (action: caught, consequence: ran ) 기 때문에 : it means "because" always ex) 잡기 때문에 도망간다. it runs away because I catch it. 치아 아쁘기때문에 못 먹는다 I can't eat because my teeth hurts!