"Don't worry, you can trust me."
Life does not always play fairly. Some people are born with a bad hand, and instead of accepting it, they find a way to improve it. Sometimes people are born with personalities or interests that don’t seem to match anyone around them. Instead of being alone, they learn to create new ones. They find who people like, and they impersonate them, sometimes even convincing themselves that they are that person.
To blend into the crowd.
When done safely, The Imposter will always be able to come back to themselves. At least they will know who they are even if no one else does. Sometimes they can have multiple roles they step in an out of flawlessly, fooling everyone around them. These people do great in sales an undercover spies or cops. They seem to have a knack for being the person everyone wants them to be. They learn to build trust, and then when needed, they learn to disappear, finding themselves in a new persona.
To be discovered as a liar.
On the other hand, the self is a powerful thing. If taken too far, The Imposter can lose themselves among those they pretend to be. Without the guide stone of who they are, they can destroy any real relationships they might have and even drive themselves mad in the struggle to get back to who they were.