This is part of Anne Frank's final diary entry only a few days before she and her family were betrayed and deported to concentration camps. In it, Anne reveals and describes the two sides to herself:
I'm split in two. One side contains my exuberant cheerfulness, my flippancy, my joy in life and, above all, my ability to appreciate the lighter side of things. […] This side of me is usually lying in wait to ambush the other one, which is much purer, deeper and finer. No one knows Anne's better side, and that's why most people can't stand me.
This can be taken many ways, but the contradictions are discussed less directly in the rest of her diary, and often include the difference between the little girl she is and the adult this horrible situation forces her to be. There is the contradiction between the young and innocent girl, and the beginnings of a young woman who is beginning to discover her sexuality and to ask questions as adults would. And finally, the contradiction between the two sides of her personality: the side that is joyful, young and happy, and the pensive, moody deeper side to herself. These two parts of her were often in conflict with each other.