Having been born/brought up in germany, where religion is almost a nontopic, I always read Science Fiction/Fantasy and always felt inclined to rational decisions. In my 12/13th year of school I had an exceptional good philosophy teacher, and found myself to find Utilitarism on some level logical. Again some years later (some before the time of the comment) I finally updated my mind/made the rational conclusion:
I should choose the most efficient path to reduce suffering in the world. I saw only two conclusions, getting really rich or becoming a successful uncorrupted politican. Since I was to lazy, felt not being able to assign relevant probability to reach either of these goals, and did not want to overthrow my other ethical views (dont become a power-hungry-politician or bad capitalist) I did not pursue it further. I started to study mechanical engineering, it gives like, A LOT of money and will enable me to further suffering-reducing technology.
Then I stumbled upon Eliezer Yudkowskis argument: most bang for the buck/euro by accelerating FAI. A better writer than myself wrote:
" I felt my entire ethical system restructuring over the course of about five seconds - a very peculiar feeling, let me tell you."-and lost focus again due to having a completely broken motivation system and psychological problems- I am running on even faultier hardware than most. I am working on both topics now. Around nine months later I discovered HP-MOR via TV-Tropes-recommended FanFics and voila- here I am. Right now I am taking my time to decide wether or not I really assign FAI à la Yudkowski any relevant probability or its just a lazy excuse, and wether its cultish salvatory-aspects do worry me or thats just some kind of bias. Updating ones mind is hard!
To break up the awkward silence at the start of a recent Overcoming Bias meetup, I asked everyone present to tell their rationalist origin story - a key event or fact that played a role in their first beginning to aspire to rationality. This worked surprisingly well (and I would recommend it for future meetups).
I think I've already told enough of my own origin story on Overcoming Bias: how I was digging in my parents' yard as a kid and found a tarnished silver amulet inscribed with Bayes's Theorem, and how I wore it to bed that night and dreamed of a woman in white, holding an ancient leather-bound book called Judgment Under Uncertainty: Heuristics and Biases (eds. D. Kahneman, P. Slovic, and A. Tversky, 1982)... but there's no need to go into that again.
So, seriously... how did you originally go down that road?
Added: For some odd reason, many of the commenters here seem to have had a single experience in common - namely, at some point, encountering Overcoming Bias... But I'm especially interested in what it takes to get the transition started - crossing the first divide. This would be very valuable knowledge if it can be generalized. If that did happen at OB, please try to specify what was the crucial "Aha!" insight (down to the specific post if possible).