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).
My family is Jewish and we all went to a Reform synagogue. This sect of Judaism is very liberal in the scheme of things, making it very clear that the bible is not literally true and accepting of just about anything, even agnosticism (if not atheism).
At the age of 16, Reform Judaism has a confirmation ceremony where one makes a statement of faith to the assembled congregation. I realized that I couldn't go up in front of a crowd and in good faith profess a belief in God. I had understood all of it to be just stories for a long time, at least since the age of 13, but I hadn't quite realized that meant I was an atheist. I just never really thought about it, but when I finally did it seemed obvious in retrospect. I ended up reading a poem to the congregation and it was very well received as it was the shortest speech given that day.
The next year, I decided I wasn't going to go to synagogue for the High Holidays (where my liberal synagogue had 3 hour long worship services). My parents weren't quite sure how to react, but they told my grandparents and my grandparents responded by deciding they weren't going either. This particular decision set off a chain reaction where it was determined that no one in my family from my grandparents on down were believers and we had all just been going along for each other's benefits. On the holidays now, my 92 year old grandfather always mentions how nice it is that the holidays give us reason to get the entire family together.
Every now and then I hear a story about (or meet in person) someone who not only left but managed to deconvert their whole family.
I wish, so dearly, that I could devote the time to at least seriously trying that...