How long will you really know a person???

it depends on the chemistry between two persons how much time do they need to reveal oneself in front of the other,it can take one month or may be one year or may be more,sometimes it happens that when we meet a new person it seems we know that person and sometimes in our own household dspite living along with persons after so many years we do not understand that person,so it all depends on the compatibality of two persons