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 have very few memories of my childhood (or indeed anything older than a few weeks), but perhaps the turning point I remember was in Lutheran confirmation school when the priest was discussing conscience. I realized that the notion of God was actually superfluous and everything that had been said would stand as well without it. After this I looked at every discussion and explanation with different eyes and soon lost my faith, although I dind't officially leave religion until four years later after high school.
I was never very religious, probably because my family belongs in church but that doesn't really show in daily life. Still, I did believe and getting rid of that made did a big difference. My mother has told be that at some of the first years in school I was confused because I had asked her about why world exists and been told about Big Bang and in the school the teacher had told that it was greated by God. So I might have gotten a few years of hints before getting it. :)
Currently I'm studying theoretical physics and until recently my rationalism has been what Eliezer would call Traditional Rationalism and what you get from scientific education, but it has been changing since I discovered Overcoming Bias and especially Eliezer's posts. They've been mind-expanding to read, I'm in debt to all of the contributors. It remains to be seen if I can actually turn them into pragmatic results. Hopefully LW can help me and everyone else on that journey.