From planning to problem solving, internal conflict resolution, and evaluations and judgments of self and others, we communicate with ourselves through intrapersonal communication. All this interaction takes place in the mind without externalization, and all of it relies on previous interaction with the external world.
Even though these thoughts happen privately in our minds, they are influenced by our past experiences and interactions with the world around us. In other words, the way we think internally is often shaped by what we have learned, seen, and experienced.