When Siddhartha is reflecting on his conversation with Gotama, he decides that teachings cannot be communicated. Why does he decide this? What does he wish to learn from him?

Siddhartha's decision to leave comes from something inside of him..... the desire for self-knowledge. He believes that to stay means giving up on what he really wants to learn, and he comes to the realization that what he wants to learn cannot be taught to him by a teacher..... it must be learned within himself.

"I will learn from myself, be my own pupil; I will learn from myself the secret of Siddhartha"