The word ‘ I ‘ is an interesting word. In the mind it means a variety of identities. Fiction and non-fiction.
Often a man missreads his own mind, and assumes that his imagined person is really who he is. The human mind is imperfect. It cannot filter out lies and deceptions automatically like a proofreader.
How do we know who we are? A man led by the Holy Spirit can know. The Holy Spirit is the Spirit of truth. He will tell us everthing we want to know about ourselves.
A Christian has the mind of Christ. He knows all things. The prerequisite is : he must be born again by the Spirit of Christ, and his mind renewed by the Holy Spirit quickened words of God. He sees and hears in his spirit, walking by the Spirit and not by his mere five senses.
He knows who he is in Christ.