The word 擅长 is formed by combining two characters: 擅, which carries the meaning of "being good at" or "having authority in", and 长, which means "long" but in this context conveys the sense of "a strong point" or "specialty". Together, they create a conceptual blend where 擅 provides the notion of skilled mastery and 长 provides the notion of a pronounced, enduring area of that skill, resulting in the composite meaning "to be adept at" or "to excel in".