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).
On one account, our rational brains exist to provide convincing rationalizations for our actions for the benefit of other people. Often the stories we tell ourselves are a lot of cobblers.
E.g. We invaded Iraq to the Iraqui people can be free, or to get rid of the weapons of mass destruction (not because of their oil!).
I will try to tell the true story of my conversion from religion.
I was about 12 years old. My parents were forcing me to be 'confirmed'. As part of this I had to make various affirmations. At that age my brain, incited by various hormones, was waking up from the slumber of childhood and beginning to feel the need for autonomy. My reaction was simple: my parents had the power, through threats and violence, to force me to do what they wanted, but they could not control what I believed. I still remember the moment of 'confirmation' - I said the words but I did not believe them.
From that time on, I thought of myself as an atheist, but I retained a fascination for religion. Some of my best friends are religious to the point of having theology degrees.
It was only when I read Nietzsche that I realized that, like most people who thought of themselves as atheists, I had not really shaken off Christianity. One thing about Christianity that proved hard to shake off was the notion that feelings can be sinful/evil.
A year reading pre- and non- Christian writings has helped to remedy that somewhat. Read Homer and see what a different world we live in post-Christianity.