I remember being twelve or so, staring intently at the communion tabernacle of our Catholic church, going through the following reasoning:

The priest physically transmutes the bread and wine into the body and blood of Christ during the sacrament of Communion. This much is an article of faith and thus will be treated as a fact. The transubstantiation occurs at the moment that the gong is struck.

Will any empirical test verify that the bread has been transformed into flesh? I must assume no, because the appearance, taste, and other apparent physical properties are unchanged.

Therefor, there must be some spiritual essence inherent to all objects which imbues those objects with a kind of metaphysical identity beyond the apparent identity one would derive from the object's physical properties!

...

I tell this story to illustrate that there are many different values of "I have always thought this way." This story demonstrates what happens when a natively reductionist mind finds itself in an epistemically hostile environment; the mind ties itself in knots trying to justify what it believes and its up basically reinventing Dualism, explaining a priori why you won't find the dragon that I know is in my garage. I have always been sharply aware that a little rationality and intelligence are a dangerous thing. In order to be anything like an "operational rationalist" I needed access to the full toolkit which I would summarize as "reductionism with some kind of parsimony prior, ethical consequentialism, a cultivated reflex toward dissolving questions, a cultivated gag-reflex against as improper use of language, aggressively checking that my beliefs pay rent, a Bayesian Positivist stance if not necessarily complete certainty in the framework, and a healthy appreciation of the fact that System 1 is really doing all the work anyway and System 2 is, at best, high level consistency checker."

I'm not even sure of any of these things I put in that list. Maybe in ten years I'll read this again and say, "Oh, stupid, that's why I made so many mistakes when I was younger." It just seems from my current point of view that all these mental tools interlock and help with "winning."

I have always self-identified as being smart, smarter than the people around me. I love to know and understand things, because this supports my self-image and self-esteem, so I've read a lot on a lot of topics throughout my life. I love telling people about the interesting things I know because this is a high-status activity and causes them to like and respect me.

Overcoming Bias and LW have a strong theme of glorifying intelligence and presenting rationality as a better or ideal kind of intelligence. When I discovered them, I naturally started reading them and eventually embraced some of the LW core ideas, which let me feel smarter or more 'rational' than others, and let me participate in the local LW meetups, which are full of very smart and interesting people I enjoy associating with.

The above is what I think the causes for my behavior are; it's my attempt at a Hansonian analysis. Obviously, I believe the ideas of rationality are both true and useful. But that's just how it feels from the inside. I don't behave very rationally, and then I blame biases and imperfections like akrasia, which are excuses accepted by this community. I use explicit reasoning to arrive at new beliefs which I then profess, but they don't always progress into aliefs that I regularly act on.

(Not particularly rationalist here, but.] In my case, it was a series of unpleasant things over which I had no control. When we were about 6, our parents had to send my sister and I to live with grandparents (due to financial uncertainty.) We mostly liked it there, though gr.-p. often had loud quarrels (to this day I hate shouting most of all. It helped, when puberty ended, to argue calmly.) Yet I had a recurrent thought - what will happen when our grandparents die? And I was revolted with myself so much I flat out decided not to think it; but later, when we were shipped back to our parents and it became safe to think again, I returned to it. I know what a resolution to omit something in my head feels like.

We returned to our parents at the adult age of 12, into a different country with a different language (Ukrainian) taught in schools, a different moral in history lessons, different everything. We had each other, and a raging case of Us vs. Them. It took years to admit to myself that maybe I don't have to completely break the way I think to fit in, mostly because we changed schools and were blessed with having an extraordinary biology teacher. (It was then that I learned the value of belonging to a group with common interests, and it shaped my life choices afterwards.) Our father is a physicist, and very pedantic in speech, which we tried to follow as a model. It didn't endear us to our classmates, which gradually showed us the weaknesses of being untimely pedantic. ...in college, I had a hothead friend who passed judgement on people quickly and forever. I vaguely understood he was wrong in this; and was at once assigned his 'conscience', for a short while. It made me willing to at least hear the other party out. ...I realize this sounds like a cliché, but being an atheist among Christians was useful, too. I had many opportunities to not let the argument be swayed into religious disagreements, or to leave when it was beyond me.

I think it's just a disposition for the most part. I became an atheist fairly young and was linked to Overcoming Bias about 2006 and the worldview really "clicked" for me. (I personally shy away from the "rationalist" label because it seems a bit self-aggrandizing.)

It also seems that I was always thinking like that. But I don't really know if that is really the case or if it's just the way memory works. Anyway, I'm going to tell the things I remember that may be relevant. Everything started with reading. I was taught to read since I was three and I liked it almost immediately. You don't need to ask your parents to read you what was next in the story. That's great! Also, dinosaurs. I really liked dinosaurs and I got quite a few books about them. When I went to the first grade, I've been somewhat familiar with the geochronology, when did different dinosaurs live and so on. I've also been given a great book about the history of biology, and I was a fan of J. L. Cuvier. The school I got into had a very nice biology classroom, in our first day they let us look into a microscope and showed us a few other interesting things. When I came home I asked my parents to buy me a biology textbook. My father decided botanics was boring, so he bought me a really interesting seventh grade zoology textbook. A few results (apart from lots of fun I got) was that I had a grasp of evolution at seven and also that I expected the world to make sense and the science to be able to discover and understand it. That was also helped by getting a few books about the history of electricity and similar stuff. The middle of the nineties in Russia was a so-called Spiritual Revolution. With the government control of ideology null and void, the media space was filled with conspiracy theories, cults and ancient miracles. While I didn't doubt their existance, as a lot of sane people were convinced these were true, I was sure they still somehow make sense. This feeling was one of the reasons I really got into one New Age book I'm not going to name. Well, my trust in books that were not obviously fairytales was the other one. Actually, the book was surprisingly reasonable. The main idea, aside from a description of a cool Planescape-like setting that was a half of the book went somehow like this: people sometimes have mystical experiences. These experiences are evidence for existence of their substance. These experiences together with the observable natural phenomena with a lot of traditions, tales and distortions compose a religion. But to remember the experiences right, to describe them using usual human terms and to make sense of them is so difficult that the kernel of truth is actually quite small. There are only two ways - to try getting these experiences yourself (something like they call a mystic's path) and to collect experiences of a lot of different cultures and search for the common features that are not explained by common human biases like anthropomorphism (an occultist's path). This made much more sense than just "our religion is the right one, all the others are wrong". A completely unrelated features of that time were a Spiderman cartoon and a book about biotechnology I was given. They told me there is a cool thing called genetics (the history of biology book was really old, and the last stories there were XIX century), so I went to the library to learn about it. That was probably the time I got my transhumanist leanings. Fifth grade, probably. The New Age book was surprisingly reductionistic, which was really nice for a young science fan. There was talking about the worlds with different number of dimensions (I looked up the geometry later) and parallel time streams. The author believed evolution was true. Souls were matter, there were laws for them, and even the afterlife was decided by the soul's "density" where it got into a place with the most similar spiritual "density". With all the caveats that this "density" is a methaphor. And the author explicitly told that if science tells us he was wrong anywhere, then he was wrong, and this admission was a huge point in his favor. I guess in my childhood this book has played the role of sci-fi. I wasn't sure I will be able to achieve any mystical experiences myself. And my grandmother, who was the best conversation partner about this kind of stuff ever was often saying that I shouldn't experiment on myself before later, so out of respect I didn't. And I was curious and I really don't believe most people here aren't going to go and investigate this kind of info if they believe it to be real. So the second path was the preferred one. I never really thought that magic is something unintelligible in principle, just something that the wizard already understands and I don't. Yet. So yes, I was investigating these things a lot. Well, until I finally found that it's quite easy to make people believe stuff without a shred of evidence as long as it makes a good story, moves their soul and is comfortable. Or frightening, that also works. And the spiritual experiences have a common thing. That is, they're human, and they may be and probably are some common bugs in human algorithms. They can even be induced by chemicals, of all things! That was also the time I've reinvented memetics. Which explained a lot of common features of the biggest religions. A little bit later I learned about the existence of creationists. No, really. I've heard about them before, but I was sure there wasn't anyone left, except maybe in some really wild places. I've joked I thought creationists were a tale mothers use to scare little biologists. This was a really vivid demonstration how people can be wrong about simple stuff. Add to this the info about the contemporary cults believeing their leaders do miracles like ressurecting people. If you remember my relations with the evolution theory you're going to understand I was afraid I may be wrong about something as simple as the young-earthers or these cultists are. In the college I tried to learn about the best reasons to believe in God and found them... well... not convincing at all. So, epistemic rationality, learning about human biases and atheism. And there's probably no really cool afterlife for everyone after they pay for their sins. And that seems like a problem that needs a solution.

Relevant: Tell Your Rationalist Origin Story

Here's mine:

Hello, everyone. I feel that I have taken an unusually circuitous route to becoming a rationalist. I started out close to rationalism in ideaspace, went really far, and then came all of the way back. I have to begin by saying how rationalism was 'epistemically proximal' to my early beliefs. After that, I'll show how far I went. Then, I'll show how I came back.

I think it can be said that my intellectual influences have been relatively epistemically favorable. I think it all started with the film adaptation of Jurassic Park when I was a kid; I think that it made me find joy in the merely real. If dinosaurs are that awesome, and they were dead and science brought them back, then science must be awesome! Then I became interested in outer space and all of the other things that kids automatically love when they love science. When I was older, like many others, I sometimes felt the urge to write science fiction. If I remember correctly, I was researching terraforming for one story, and then I came across a Wikipedia reference to Robert Freitas' respective estimations for how long it would take biological organisms and nanotechnological machines to sequester all of the carbon dioxide in the Venusian atmosphere. That led me to his book Xenology. Therein, he discussed various alternative forms of government that alien civilizations might use, and mentioned Robin Hanson's work on idea futures/prediction markets, proposing a form of government based on prediction markets called "futarchy." I didn't follow the Wikipedia page to Overcoming Bias, which really sucks because I think that this was right around the time that Eliezer was still posting on OB what later became the sequences, or around the time that LW was coming about.

Later, I got into lifehacks like mnemonics and speed reading and stuff, and I found the list of the best textbooks on every subject. I still didn't become a user or even a lurker.

Then, less great things happened.

I became an intellectual contrarian and decided that people hadn't 'given enough credit' to psychodynamic psychology and the historical contributions of psychoanalysis. It didn't help that there were people supporting this who are Nobel laureates and have written leading texts in the field of neuroscience, or that a lot of people are trying to shoehorn Freud's theories into neuroscience. Then I became a meta-contrarian and decided that Lacan was, as Prof. Chomsky would put it, a conscious charlatan, but that Sartre was alright. Then Sartre got me into existentialism, and existentialism got me into continental 'philosophy' in general. I decided that analytic philosophy (read: philosophy) and science were imposing themselves upon a domain in which they did not belong.

During this time, my friend, who is a huge Harry Potter fan, showed me Harry Potter and the Methods of Rationality. I was like, "That's cool," and didn't read it.

For a reason that I can't remember, I ended up looking up the textbook list again a few days ago, and, fortunately, I thought: "This is my fifth time here in as many years and I haven't seen what they have to say. Maybe I should give it a shot." And then LW convinced the everloving hell out of me.

I was pretty much always this way, except way more overconfident in conclusions and underconfident in myself. It took failing a lot and succeeding in bigger things to cure both of those even part-way. I got a big dose of Outside View when I hit college.

Of course, I didn't come pre-loaded with the formalism, but a lot of the time (definitely NOT all the time!) when I encountered the formalism it was 'okay, now I've seen that written out'.

Spock was an influence, but may have been more of a 'you too'.

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.

This depends on what you mean by "rationalist." If you mean having certain opinions, there will always be a backstory, since acquiring opinions is a historical process. If you mean being interested in rationality and biases and so on, there will always be a backstory, since people's interests develop over time.

If you mean the characteristics that make people want to be reasonable, I suspect that most of these are personality traits and in that way people will have "always thought that way." This is just as true of extreme personality traits as of non-extreme ones.