1. Historical and cultural symbol: Chang 'an is the capital of the Tang Dynasty, representing the prosperity and glory of that era. In this idiom, "Chang 'an" symbolizes the prosperous times of the Tang Dynasty, and "Three Wan Li" is a symbolic number to describe the distance between reality and ideal.

2. Dream Pursuit: The "Three Wan Li" also symbolizes the dream pursuit of Chang 'an in the prosperous Tang Dynasty, representing a long and challenging road to the ideal.

3. Strive to realize the ideal: "Three Wan Li" is interpreted as striving to realize the ideal. This distance represents the closer to success, the more difficult it is, and the more serious it should be.

4. Different paths and challenges: In the Tang Dynasty, if people wanted to realize their ideals, such as entering the DPRK as an official, they needed to go through different channels, such as imperial examinations, enrollment, inflow and outflow, and each path had its own specific challenges and difficulties.