It expresses the sadness of not seeing the beautiful scenery in time and the person you like, that is, being separated from the person you like.
To miss the ancient meaning of Chang 'an is actually to miss something that you think is very important, just taking Chang 'an as an object of expression. Moreover, this sentence is an ancient sad sentence, which can be used to make your own personal signature, and can also be used to copy your circle of friends who send social platforms.
The ancient meaning of missing Chang 'an means that missing is a lifelong regret, and missing is the regret of many people, but missing is missing and may never come back. This is also the meaning of this sentence.