I’m used to hearing this played a lot faster; I think it was Nelson Freire’s version I heard first. Horowitz takes this slowly, fusing what Wikipedia calls a “fluttering harp-like broken triad accompaniment” and a “spacious and languid melody” into a texture. The chords emerge delicately out of the accompaniment at the beginning; the piece becomes much more dramatic; things settle into a “relaxed flow,” but nothing is relaxed. The song seems a bit bittersweet to this listener, and the relaxed feeling one might have as a listener comes from trying to figure out what is happening with every note. Each note sounds distinct; relaxation is a consequence of exhaustion, the attempt to just appreciate brilliance.