Since I don't know the movie well, I'd say it might be about isolation. The title gives the impression that the protagonist is in a state where no one is aware of their existence, which often leads to themes of loneliness and self - discovery.
It could be very significant. Since it's based on a true story, it might show how a person can exist in a state of anonymity even though they are part of real events. Maybe it's a story of someone who was overlooked or not given attention during certain real - life events. It could also touch on themes of self - discovery within that state of being unnoticed, like how the person coped with being in a situation where nobody knew they were there and what they learned from it in the context of the true story.
It could be that the person has just moved to a new and very quiet neighborhood. They haven't made any friends or contacts yet, so it seems like nobody knows they are there. Also, if they work from home and don't go out much, this would contribute to the situation. For example, they order groceries online and have no need to interact with neighbors on a daily basis.
I'm sorry, I haven't actually seen this movie. But generally, a movie with such a title might be about a person who feels isolated or hidden from the world. It could be a story of someone's inner journey while being unnoticed by others.
Maybe it's about a child who is often left alone in a big house while the parents are busy with their own lives. The child feels like nobody knows they are there, and this is based on a true family situation. There could be small incidents in the house that the child experiences alone, and these incidents build up to a story of loneliness and self - awareness.