Grammar
-(으)ㄴ 적이 없다
to have never done something
Form
Verb stem + -(으)ㄴ 적이 없다 (“have never done”).
Function
Denies having ever had a past experience, rather than merely denying an action at a specific time.
Why this form?
-지 않았다 — “did not do”: denies an event; -(으)ㄴ 적이 없다 denies any experience of that kind.
Forms not to confuse
-지 않았다
어제는 가지 않았어요. — I did not go yesterday.
Examples
그 사람은… 저를 한 번도 좋아한 적이 없었어요… — That man… never once liked me…
그를 만난 적이 없어요. — I have never met him.