If you assume people won't find another way to kill themselves
I've seen something about this that Google showed me is discussed here. It works out that one in three people who would have killed themselves with gas found another method, and the other two thirds just didn't bother. Ideally I'd find some other statistics along this line, but since I'm lazy and I don't actually care all that much about this issue, I'll just go with that. Accounting for this, and not accounting for people find another way to kill others, there's still a little more suicides caused by guns than homicides.
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.