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.
If it was true that 99.5% of candidates fail the FizzBuzz test, then someone who passes it is better than 99.5% of the candidates who get to the interview stage, and should be hired immediately for any computer software job they try out for (unless you believe more than 100 people on the average get interviewed before anyone is hired) . The experience in the job market, of people who can pass the test, does not bear this out.
What you're missing is the following insight:
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