Aaron: After his enlightenment, the Buddha reflected on what could be shared with others, to try to find some concise format in which to express it. The formula that came up for him is this Four Noble Truths. He based it on the way a physician visiting a sick person would state what he had learned. What is the problem? What is the cause of the problem? What is the possible outcome, and how do we move toward that outcome? This was a prescribed formula of his day, in which a physician worked.
So, the first: what is the problem? There is suffering, dukkha. The word ka in Pali means the hub of a wheel. Du means “off-center”. Thus, dukkha is the wheel that is off-center. Conversely, the prefix su means “center”. Sukkha is happiness, the wheel that is centered.