Intrapersonal communication helps one

Intrapersonal communication helps one learn about oneself through inner dialogue and reflection.

Talking to and listening to oneself builds self-understanding.

Knowing what others are thinking would need communication with those others, not within the self.

Communicating with the general public is mass communication, outside the inner realm.

Becoming a talented public speaker is an outward skill, not the self-knowledge this fosters.

Intrapersonal communication is the communication a person carries on within the self.