The idiom of picking up flowers in the morning and picking them up in the evening means: flowers that fall in the morning are picked up in the evening. It is a metaphor for revisiting the past and bringing up old things again. The quote comes from Lu Xun's work "Morning Blossoms Plucked at Dusk".

The meaning of the setting sun is: the setting sun is the sun that is about to set, and the setting sun is the decline and decline.

The flowers that fall in the morning and the setting sun are picked up in the morning are like the flowers that have fallen in the morning. They are picked up at night and are like the sun that is about to set. It is useless. My understanding, I hope it can help you.