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).
As far back as I can remember I have wanted to be a scientist and to walk the path of rationality. What comes to me as a watershed moment was when I was 15 or 16 an my very Christian Grandfather came to visit. He told me that since I had a very scientific mind, he was giving me a scientific gift. It was a thin book with a title something like "Scientific Proof of the Bible".
Afterwards I remember sitting for what felt like hours in my room, staring at the closed book. "What if I was wrong?" I kept asking myself with dread. What if there really was scientific proof of the existence of God and what I had always taken to be the nonsense of the Bible? What if going to church and praying really WERE things I should be doing? If so, how could I justify not going. What was the guiding principal of my life, anyway?
In the end, I decided, my guiding principal was "Truth at any cost." If I was wrong, I wanted to KNOW I was wrong, and I would deal accordingly. So, I picked up the book and started reading, and within a few minutes I was laughing in relief as there wasn't a cogent argument or scientific proof, or even the slightest bit of rationality in the entire thing.
But my Grandfather had given me a great gift, although not the one he thought. From then on, I was willing to lose arguments since my desire was to know the actual truth, and not to merely have the comfort of thinking I was right. That, as they say, has made all the difference.