Most of the discussion posts I've written have led to me changing my mind, but that's pretty me-specific :P

Near every time someone has given me a book recommendation. For example, I asked a question in an open thread that led to me reading "An introduction to tonal theory," which then proceeded to change my mind.

Discussion of habit formation here has been really useful to me, I'm not sure how much of this is "changing my mind" vs. "learning new stuff." I guess I'm pretty bad at making that distinction in general.