2. Behind the front ring: flip cover; Caution is prevention. The failure of referring to the past can be used for reference by the future.
3. The sound of the rear car: a warning to the rear car. A metaphor for previous failures or setbacks can be used as a reference or lesson for future work.
4. Reviewing the past and rejuvenating the present: refers to rejuvenating the modern with a reference to reviewing the past.
5. Lessons from the past: Take past mistakes as a reference, and act cautiously in the future to avoid repeating the same mistakes.
6. Take people as a mirror: take the success or failure of others as your own reference.
7. Lessons from the past: Take past experience and lessons as reference for future work.
8. In view of this, learn from it. Learn from it.
9. Start today: Start studying today. Learn about the past as a reference for today.