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).
I don't remember any sudden move towards rationality - I was raised in a godless household in a mostly godless country (France). I've always been pretty interested in science-fiction and in religion (though not as something I might believe in).
What pushed me a bit more towards rationalism:
Maths classes that required a lot of demonstrations (and having to be able to do them again on the blackboard with an examinator)
A physics teacher who insisted that we always include an uncertainty factor throughout our calculations, and not give excess decimals (I've noticed that I tend to think in terms of probability distributions more than others around me)
Questioning a lot of my political opinions, and noticing when my brain was "up to no good", for example when EvaluateAsLeftWingOrRightWing(idea) was being called before EvaluateTruth(idea).
Getting annoyed with atheists who consider religion to be the only domain where one can be irrational
Working as a programmer, which doesn't leave much place for wishful thinking
Reading Overcoming Bias daily
I wish some of the programmers I've worked with realised this.