For me lurking on ADHD sub-reddits. I noticed a few people were giving advice that worked so well or made so much sense, that I looked at their profiles and saw they were heavy in autism communities.
Then I watched this 5 minute video and cried for 3 hours at how fucking seen I felt. https://www.youtube.com/watch?v=cTzUbe5hoI8
He led a very different life from me and yet I related to aspects pretty easily.