According to the renowned historiographer Liu Zhiji （661-721）of the Tang Dynasty, those who study and write history must have three strengths, namely, the ability to compose historical works, rich knowledge of history and historical materials, and deep insight that enables them to analyze and evaluate history. Liu believed that deep insight in analyzing and commenting on history was the most important of the three qualifications.

A historian must have three strengths. …The three strengths are talent, learning, and insight. （The Old Tang History）