Reviewing the past helps us understand the present and predict the future. It is also said that “reviewing the past we understand the future” and “knowing the past we understand the present.” The Chinese word jian (鉴) can mean “mirror” and hence to “review the past” as if in a mirror, “understand the past,” or “gain knowledge of the past.” The lessons of the rise and fall of dynasties and states, the words and deeds of historical figures, as well as right and wrong, and good and evil, help govern the country and improve personal morality. “Understanding the present,” “reviewing the present,” or “understanding the future” means predicting the future based on the present. The rulers of antiquity saw it as extremely important to draw lessons from history in order to avoid past mistakes and justify their policies by making them conform to the needs of the country and people. The concept of “reviewing the past to understand the present” stresses both the practical significance of history and the historical depth of things present. It is similar to the concept that “past experience, if not forgotten, is a guide for the future.”

It is advisable to review the rise and fall of previous dynasties and the achievements and failures of the present dynasty, to commend the good, condemn the evil, and adopt what is right and discard what is wrong. (Sima Guang: Memorial on History as a Mirror)

It is of great importance to review knowledge of the past to help understand the present, expel the invasion of the State of Wei and wipe out the State of Wu. (A Peace Banquet)