The setting sun with the curtains still and the flag depicts a quiet scene, contrasting the "infinite sadness" (turbulence) caused by wandering and leaning, climbing the stairs and relying on danger.
"The curtains and flags" "The sunset is late". This sentence is the most colorful stroke in the description of the scene in the whole poem. It seems ordinary, but in fact it is delicate. "Curtain flag" is the close view, and "the sunset" is the distant view. The close view and the distant view merge into one. It can be imagined that the poet's sight changes from Scanning from near to far, gradually letting go, blending into the vast twilight. The motionless curtains indicate that the lake is calm; the late setting sun reminds the tranquility of the evening. How can such a poetic and picturesque situation not arouse the poet's richness? Where are your reveries?