Why was Siddhartha unhappy?

Siddhartha felt that there had to be more to life than just living comfortably as a Brahmin. He had learned much from his father and other priests but Siddhartha longed to know even more. He had begun to doubt the usefulness of the sacrifices offered to the different gods, and he was unsure how these prayers and rituals related to the Self or the Atman.