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.
But when you go to many worlds you lose the Born probabilities, doesn't that bother you? The Born probabilities are the actual measurable predictions of the theory.
Many worlds is only simpler as a theory if you don't include a measurement postulate, in which case no one knows how to get Born probabilities.
You can postulate the Born probabilities, but now the theory is exactly as complicated as it was before, so there is no reason to choose many worlds over something like consistent histories.
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.