It is not a repetition, but a step-by-step reinforcement. When I was in college, my classical literature teacher believed that there were "ten tragedies" in this couplet.
One sorrow: a guest; two sorrows: a frequent guest; three sorrows: a frequent guest in autumn; four sorrows: a sorrowful autumn, a frequent guest; five sorrows: thousands of miles of sorrow, a frequent guest in the autumn; six sorrows: on stage; seven sorrows: The Eight Sorrows: Stand alone in the midst of illness; The Nine Sorrows: Stand alone in the midst of multiple illnesses; The Ten Sorrows: Stand alone in the midst of a century of illness.
"A sad autumn for thousands of miles" is a calendar space, "often a guest" is a calendar time; "a hundred years of illness" is a calendar time, and "alone on the stage" is a calendar space. Therefore, this couplet is very neat and rigorous as a duality. The earthly arrangement combines the spatio-temporal relationship of heterogeneous melancholy.
The "autumn" here must be "sad", so the "sad autumn" here is not more sad than "autumn". For example, autumn, which means the joy of harvest, is not the scope of this poem at all; the "stage" here must be "alone"
This is a work that describes the sadness of "visiting" and "climbing a building". There are many stories from ancient times to modern times. This combination of Lao Du builds ten layers of desolation around two centers. The order when reading the poem is from front to back, but the order when thinking about it needs to be from back to front. ", with each additional modification, the degree of sadness doubles or even tenfolds. Until the two extreme numbers "thousands of miles" and "hundred years" appear, a sense of solemnity and desolation fills the poem.