This is a metaphor. People should remember the previous experience and lessons as a reference for future actions. From "The Warring States Policy" Zhao Ceyi: "The past is not forgotten, and the future is a teacher."

During the Jin Dynasty, Alina Zhang, an adviser, told a passage of Zhao Xiangzi, one of the "three doctors", before resigning from his post and retiring.

Manual adoption (づづ 3 づ).