When you get to the music video, notice that the pianist plays the theme with his left hand. Then, about half-way through, the theme switches to his right hand, and then back to his left hand. I think Chopin wanted the lower notes to represent thunder and wind; higher notes, rain.
Chiasm in Music
The pianist reaches the center at about 2:38, the mirror, and the structure on both sides is the same with some variations thrown in to please the listener. For an explanation of chiasm, see the two entries on 2/7/22 and the YouTube video below the music.
Chiasm in Math
In algebra, chiasm is called ring theory, which is the study of rings, algebraic structures in which addition and multiplication are defined and have similar properties to those operations defined for the integers.
Music and Writing
Chopin composed the Etude the way a writer ought to compose a story, or an essay with an extra paragraph. Typically, an essay has five paragraphs, but here in this Etude I have broken it up into six parts as if it were an essay with the extra paragraph. First paragraph - Intro and theme; 2nd, 3rd, 4th (center of chiasm), and 5th paragraphs all restate the theme (topic sentences); and 6th paragraph - theme restated and Conclusion.
Sometimes, I follow a simple chiastic structure in a post by starting and ending with the same word or phrase.