ㄹ지 못하다

cannot; does not know

Most lines here are 알지 못하다, which is -지 못하다 'be unable to' on 알다 — a heavier, more written way of saying 'does not know' than the everyday 모르다: 그 사람의 모든 걸 우리가 알지 못한다니까, 'you can never really know everything about a person'. One line shows the genuinely different -ㄹ지...-ㄹ지 pairing: 잘할지 못할지 모르겠어, 'I don't know whether they'll do well or not'.

Register: slightly formal