This tragic point in the story of Their Eyes were Watching God represents a turning point in Janie that encapsulates the loss of her innocence. The "two different selves" that her internal dialogue represents are an inside and an outside. She now possesses a facade that she can put on for the world to see, while she will thereafter keep her most personal thoughts to herself. This is a condition that most human beings and characters, both fictional and not, are intimately familiar with. However, it is quite an alien feeling to Janie, who has before this moment always worn her heart on her sleeve, approaching the world with an endearing honesty.
With this separation comes the capacity for lies and deception, something that would have not occurred to Janie before this moment. Her disillusion with her love for Joe is something that draws the true, cruel nature of the world around her into sharp relief. The split is necessary for her to cope with the loss of this love, as if she would have stayed an innocent girl, she would have been crushed by the loss. Her two selves cannot by the very nature of having been born ever merge again, as the loss that she feels is irrevocable.