What do you mean by twilight?

It means walking in the morning fog, but suddenly falling into the sunset.

Walking into the morning fog and falling into the dusk cloud is walking in the morning fog and suddenly falling into the dusk cloud. From morning till night, from spring to autumn, it is obvious that time flies. From the author's words: gone, left, or I don't know, fog, dusk clouds, fallen flowers, autumn wind, all have a feeling of melancholy and sadness.