be in on ~에 관여하다, ~을 알다, ~와 한패다 (informal) So if the driver of the train was in on it, then the passenger did get off. 기관사가 연루된 사람이라면 승객이 내린 게 맞아. Hey, did you hear about the new project? I think we should be in on it from the beginning. 야, 새 프로젝트에 대해 들었어? 처음부터 참여해야 할 것 같아. Absolutely! It's always better to be involved from the start to understand the requirements. 물론이지! 요구 사항을 이해하려면 처음부터 참여하는게 ..