I've actually tried to track this sort of thing before. Like, periodically I'll do a Review of My Life So Far and recall specific trends in the general evolution of my character. There are usually three threads I reflect upon, which not coincidentally are things I consider important: my happiness levels, the music I listen to, and my rationalism.
In explaining the origins of my rationalism I initially thought that I just had an unusually strong aversion to appearing foolish or stupid, but now I think there's something else going on as well. For instance, when adults play games with children they tend to "go easy" and let the child win most of the time. This angered me because I knew that I wasn't really winning and so to celebrate would be disingenuous. If I was only concerned about appearing skilled, I would take the false victory in stride. Instead it seems I am especially averse to when people's actions or beliefs are incongruent with reality.
There are a few milestone lessons which led me to where I am now (you wanted long and detailed, here it is):
Age 6/7: I was really into stage magic. I had the books, I learned some tricks, I did impromptu shows for my friends and family. One year for my birthday I went to a magic show instead of having a party (totally worth it, I got to pet a python). This hobby taught me that things aren't always what they appear, that events have to have physical cause-and-effect, that I can be fooled, and that magic isn't real.
Age 7/8: By now I had pretty good heuristics for determining fact from fiction. Indeed I remember an exercise in school where we were given various books and asked to sort them into columns of Fact or Fiction, which I found to be the easiest task in the world. With this skill I readily dismissed Santa Claus, the Easter Bunny, the Tooth Fairy, and The Bible as obvious works of fiction. Oddly, some budding consequentialist in me decided that these deceptions were justified since they motivated people to be good (in the case of Santa Claus and The Bible) or were merely entertaining stories. So I wasn't upset with my parents for lying, because I understood that the mythology of Christmas etc. was fun. However, I was annoyed when they continued to try to deceive me even after I told them I knew it was all fake. One time I woke up as my father was playing the Tooth Fairy, replacing tooth with coin. He cursed when he saw he'd been caught, even though from my perspective the jig had been up for ages. I was annoyed because their behaviour no longer made sense, that I was being treated as a child despite having adult knowledge. This taught me that people could be stubborn in their wrongness in ways I didn't understand.
Age 8/9: Religion will be the major focus for a few years. My understanding of religion (and by religion I mean modern mainstream Christianity) was that it was at best a collection of fables with morals and at worst a sort of bogeyman to scare grown ups into acting ethically. But I assumed that a majority of adults didn't really, truly believe in something so obviously sorted into Fiction, but rather those that go to church do so as a sort of safety net -- "just in case" (more on that later...). One time I was at the neighbour's house playing with their kids, who were around my age. The one boy kept talking about God, as if he was a real person or something. Puzzled, I asked him if he knew God wasn't real. He became very upset and ran to his mother, who promptly dismissed me. I was never allowed back to their house. I didn't understand what this meant at the time and continued to hold onto my belief that few people were seriously religious. Of course, years later I learned about belief-in-belief and that my intuitions as a 9 year old were closer than I thought for most of my teen years.
Age: 12/13: A.k.a that one time I became agnostic for about 10 minutes. I had a paper route at this age, which in my small rural town meant a lot of bike riding between houses. That also meant a lot of time to get lost deep in thought as I let my body run on auto-pilot. On this day I was thinking about heaven and hell. I figured even though there's a very small chance of God existing, I definitely did not want to go to hell, so maybe I should become more religious, just in case. At the time I rejected this reasoning for two reasons: 1) I couldn't force myself to believe in something I find absurd, and surely God, being all-knowing, would see through my deception and possibly be even angrier; 2) What kind of supposedly just God would torture me for genuinely trying my best? The very concept of hell began to crumble here. I resolved instead to simply live a good and virtuous life because that would turn out well regardless of the existence of God. Years later I found out this argument was called Pascal's Wager and that people had been debating it for centuries.
Age 15/16: Youtube introduced me to the crazy world of religious fundamentalism and all naive preconceptions of people not taking religion seriously were shattered. For a little while I was one of those insufferable, misanthropic internet atheists. This was a pretty dark period of my life but it did lead me to learning about logical fallacies. I became obsessed with learning how people could be so wrong yet be so convinced they're right. Then I became worried about my own beliefs. How could I be sure that what I believe is true? I began to question everything. I discovered my blind cynicism had led me to believe in that conspiracy theory about pharmaceutical companies holding back cancer cures. I was terribly embarrassed by this. I had been telling my friends about this conspiracy! I had been foolish and wrong, like those crazy religious people I hated so much.
Age 17: I learned about cognitive biases, mostly from wikipedia. This was a goldmine of insight and at the time felt like it was everything I needed to know. I'd cooled down considerably on my misanthropic atheism, instead opting to be polite and kind whenever I could. Around this time I also read an entire dictionary of logical fallacies.
Age 19/20: A friend introduced me to HPMOR. I loved every moment of it and it led me to Less Wrong, which renewed and invigorated my interest in cognitive biases and beyond. At the same time I was taking a lot of psychology courses at university (to supplement my math major, naturally) which illuminated yet more corners of the human mind. I also had a graph theory professor who pushed me harder than anyone to be more rigorous in my proofs. To him, nothing was "trivial". It was as infuriating as it was imperative to learning to be as vigilant and thorough as possible when thinking rationally.
Now I'm 23 and I've read most of the Sequences as well as Slate Star Codex. I also took Dan Ariely's online course on behavioural economics. I guess I fall more into the "I was always this way!" camp but as I look at all the gradual steps I took it's hard to imagine that anyone, even Ariely, could have a single eureka moment which shifts their entire mindset. And thinking about my other "extreme" character traits, none were (from what I can tell) originated in some extreme experience. But that's just me. I do know a guy -- an extremely muscular, fit guy, at that -- who screams in terror at the sight of grasshoppers because when he was a child a grasshopper leapt into his mouth, crawled down his throat, and crawled back out again. Would very much like to see the results of that poll.
I enjoy the polls, but I'm new here and lack the karma to even vote in them (indeed, the desire to see the results of the polls is part of what motivated me to make an account in the first place). Hopefully my rationalist backstory will be interesting enough to gain the requisites! Then I can go back and vote in all the polls I've lurked in the past...
I have a similar experience with music. In my mind I can hear hugely complex compositions but in practice I'm nearly tone deaf and am incapable of transposing these sounds to the outside world. When I do write music it is always spontaneous and improvised with an instrument in my hands. I agree these must be different systems and I'm sure we can come up with other such divisions -- the gap between understanding meaning and expressing it in words, for instance. I suppose child prodigies are those with a natural bridge between these systems?
Hello LW! Long time lurker here. Got here from HPMOR a few years ago now. This is one of my favourite places on the internet due to its high sanity waterline and I thought I'd sign up so I could participate here and there (plus I finally came up with a username I like!). I've got a B.Sc. in math with a concentration in psychology (apparently that is a thing you can get, I didn't know either) and my other passions are music, film, humor, and being right all the time ;)
Thanks to LW and the rest of the rationality blogosphere, I've added effective altruism to my life goals. I've been wondering lately how we might shift the cultural norm from "boy I sure hope I have a big house and drive a fancy sports car by the time I'm 30" to "boy I sure hope I'm donating lots of money to worthy charities by the time I'm 30".