"You knew all along that your sanctioned world was only half the world and you tried to suppress the second half the way the priests and teachers do. You won't succeed. No one succeeds in this once he has begun to think."

Demian says this to Sinclair during the time they are taking Confirmation lessons together (Chapter 3). Here, he lets Sinclair know that he knows how Sinclair has been thinking. Demian forces Sinclair to face just what he has been feeling about the other realm. Demian roots out Sinclair's deepest desires, and shows Sinclair how he has been suppressing them. This is a particularly psychological moment, where Demian is essentially serving as Sinclair's psychoanalyst, uncovering what lies hidden in the depths of Sinclair's being. This also foreshadows Sinclair's future development. Demian, of course, turns out to be right—Sinclair eventually becomes unable to continue to suppress his desire to break out of the holy world.