Siddhartha decides not to study with Gautama because he believes that no one can teach him what he needs to learn. Despite Gautama's reputation as a great teacher, Siddhartha feels that he has already learned everything he can from him and that he must continue on his own path to enlightenment. He believes that enlightenment is a personal journey that cannot be taught but must be experienced and discovered through one's own efforts and experiences. Therefore, he decides to continue his quest for enlightenment by following his own intuition and inner guidance, rather than relying on external sources such as teachers or texts.