I had certailny been influenced by my father, who, after my parents divorced, told me to have my own goal of life. However, I wanted to have a truly good one, not an evil one. It caused me to search for precise definition of "universal good," - a precise criterion for deciding, what action is universally good and what action is not.
I know Bayes theorem now, such a wonder! But when I was a kid, I had not such a romantic and beautiful event as Elizer had, so I came up with a different criterion. The best is to let the world exist, and the worst is to destroy the world. The "world" here refers to the universe as a whole, as well as the universe as every no matter how small its part.
Ever since I came up with this criterion, this thought didn't seem to lose its importance. In fact, I made this idealistic motto "let everything exist," which is the extropic side of this criterion.
I would say, it helped me to overcome great difficulties of life. I guess, I'm not alone, in fact, one of the posters here, Wei Dai, has a mailing list about the very idea that "that all possible universes exist" ( http://www.weidai.com/everything.html ).
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).