면 참다

if X, hold it in

-(으)면 gives the trigger and 참다 is holding something back — pain, anger, an urge, a laugh. More than half these lines are negative: 아프면 참지 말고 병원 가셔도 'if it hurts, don't tough it out, go to the doctor', 이러면 참을 수 없는 거예요 'when they do that I can't take it'. So the phrase turns up as often to reject enduring as to advise it.