Mettle is a term used to describe courage and determination in the face of adversity. It is often seen as a measure of one's ability to endure difficult situations. In this context, it is closely related to the term ability, which refers to the capacity to do something or to achieve a certain level of success. Courage is also closely related to ability, as it is the willingness to take risks and face challenges despite potential danger or difficulty. Together, these three terms form a powerful combination that can help individuals to overcome obstacles and reach their goals.