This quote suggests that if nobody shows any interest in a person or pays any attention to them, then it can cause them to feel like they do not exist. It suggests that in order to feel like you exist, you need some kind of acknowledgement from the world. This could be in the form of love, attention, or recognition. If we think of ourselves as existing only in the eyes of others, then if no one is thinking of us, then it can be difficult to feel like we really exist.