My position here is Knightian uncertainty -- I have no idea whether that's true AND I have no idea what are the chances of it being true.
That's, umm, nice, but I don't see how it helps answer the question since I suspect the number of 'not me!' would be enormous.
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.