Throughout their lives, all people go through various levels of personal development. Some are only able to wade through a few of them and then pause, stay in place for the rest of their days, while others keep going through the stages.
The latter is constantly open to receiving new information and broadening their perspective. Because, in essence, personal development is:
… broadening the perspective.
Right after birth, we have a very limited perspective. We are connected to the world. We don't know where we end or where the world begins. Psychologists refer to this impression as "ocean unity." It is, however, a very unconscious type of oneness. If we develop far enough, we go through many stages of "glare" until we finally come back to a sense of oneness with the world. This time, however, this sense of oneness is extremely conscious and is often called enlightenment.