"Jewish" means everybody who doesn't believe in Jesus. Ancient Pagans and contemporary atheists? Kinds of Jews.
I think I formed this belief very young, and I think I had my first conversation about beliefs with a Jew at 15ish, so lot of echo chambering. I updated immediately (and probably turned an interesting shade of red).
What is something you used to believe, preferably something concrete with direct or implied predictions, that you now know was dead wrong. Was your belief rational given what you knew and could know back then, or was it irrational, and why?
Edit: I feel like some of these are getting a bit glib and political. Please try to explain what false assumptions or biases were underlying your beliefs - be introspective - this is LW after all.