反客为主

反客为主

Literally means:

turn from a guest into a host

Actually means:

gain the initiative

I means a guest becomes a host, i.e. the normal positions of a guest and a host are reversed. It also metaphorically means turning from the passive side into the active side, or from a person who is commanded by others into one who commands others.

客人反过来成了主人。指违反了正常的主客关系，也比喻变被动为主动，或由受人指挥的角色，变成指挥别人的角色。