This sentence comes from a poem by Bai Juyi, a poet in the Tang Dynasty: "bloom can be folded straight, so don't wait for no flowers to fold branches." This means that bloom should be picked when it is in full bloom, otherwise, when the flowers wither, it will be a pity.
In the TV series, Zhen Xuan used this poem to express her thoughts and condolences for Guo Ziyu County, and also to express her feelings about life. She knows that life is short, cherish the present, and don't wait until it is lost to regret it. This sentence has also become one of the classic lines in TV series and is deeply loved by the audience.