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).
Disclaimer: Cognitive science says that this incident probably didn't happen the way I remember it.
When I was 5 years old, my mum sent me to Sunday school because she was casually Church of England and that's what you did. It was only the second or third time I'd been and after the lesson they had us pass around a box full of sweets and told us each to take one. I remember thinking that there was something I really didn't like about this as the box was coming around so I passed it on without taking a sweet. One of the women running the group noticed and asked the other children to pass the sweets back to me, assuming I'd forgotten to take one. I stopped them and said that I didn't want a sweet thankyou. When she asked me why I paused for a moment and then said 'I don't think Jesus would like you bribing us to believe in him'.
She gaped at me a little and there was a very awkward pause but nothing was said immediately. When my mum arrived to collect me they asked for a word with her while I waited in the car. When she came back, she sat down and asked me what had happened. When I explained the story to her she burst out laughing, told me I'd done well and that I wouldn't be going to Sunday school any more. On the way home she explained that my conclusion about the sweet was right but saying so had upset the ladies in charge, especially because I'd said it in front of the other children, and they'd asked her not to bring me to Sunday School again. This confused me because the only explanation that made sense was that I'd been excluded because what I'd said was correct but 'dangerous' in some way.
At the time I believed in god in a childish, unquestioning sort of way but I'd already had a few problems with the idea that I should believe in God because I wanted to go to heaven and because if I didn't I'd go to hell and the sweet incident was the first time I'd put my finger on the problem. If I was going to believe, I wanted to believe based on truth not bribes or punishment.
It wasn't an 'aha' moment exactly but the incident stuck with me over the years and the idea that I wanted my beliefs to be true rather than based on what I want to be true has, I think, kept me heading in the right direction.