Addition to this >>/49380/
Sometimes when other people form an opinion about us, some people find it easier to conform to what they feel is an expectation, instead of confronting. Thus the mask will be given by another.
This happens in many situations, not just in relationships. There are particular people who are too quick to judge (average people are like that), or they have an agenda and a role they want to push on others (these are more rare, controlling type of people, often just egotist, sometimes malicious, I guess narcissists, psychopaths etc.).