How do you know your new belief is more accurate than your old belief?
Hm, because I spend more time researching the issue than I had before? That should count for something, shouldn't it?
Also, I can actually explain things like decoherence without hand-waving now. Looking back there were some gaps in my understanding that I just brushed over. You could say it was a failure of rationality to give as much credence to the Copenhagen interpretation in the first place.
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.