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.
I'm not convinced there's a real difference there.
In both cases you expect that in no experiment you observe (and survive) will the gun fire and kill you. In both cases you expect that an independent observer will see the gun fire and kill you about half the time. In both cases you expect that there is some chance that you survive through many experiments (and, I repeat, that in all those you will find that the gun didn't fire or fired in some unintended way or something) -- what actual observable difference is there here?
In the pilot wave theory, the probability that you will witness yourself surviving the experiment after it is performed say 1000 times is really really small. In MWI that probability is close to 1 (provided you consider all future versions of yourself to be "yourself"). So if you witness yourself surviving the experiment after it is performed 1000 times, you should update in favor of MWI over pilot wave theory (if those are the two contenders).