According to tradition, Buddhism began with the Buddha's enlightenment. This was the spiritual awakening of one man, Siddhartha Gautama, somewhere between 528 and 445 BCE, who afterwards was called the "Buddha," or "awakened one." He then taught others what he realized, along with the methods he used to achieve that realization, and those teachings have been passed down to the present day. What exactly did Siddhartha comprehend in his enlightenment?