I remember the exact moment when I began my journey as a rationalist.
It was not while reading Surely You're Joking, Mr. Feynman or any existing work upon rationality; for these I simply accepted as obvious. The journey begins when you see a great flaw in your existing art, and discover a drive to improve, to create new skills beyond the helpful but inadequate ones you found in books.
In the last moments of my first life, I was fifteen years old, and rehearsing a pleasantly self-righteous memory of a time when I was much younger. My memories this far back are vague; I have a mental image, but I don't remember how old I was exactly. I think I was six or seven, and that the original event happened during summer camp.
What happened originally was that a camp counselor, a teenage male, got us much younger boys to form a line, and proposed the following game: the boy at the end of the line would crawl through our legs, and we would spank him as he went past, and then it would be the turn of the next eight-year-old boy at the end of the line. (Maybe it's just that I've lost my youthful innocence, but I can't help but wonder...) I refused to play this game, and was told to go sit in the corner.
This memory—of refusing to spank and be spanked—came to symbolize to me that even at this very early age I had refused to take joy in hurting others. That I would not purchase a spank on another's butt, at the price of a spank on my own; would not pay in hurt for the opportunity to inflict hurt. I had refused to play a negative-sum game.
And then, at the age of fifteen, I suddenly realized that it wasn't true. I hadn't refused out of a principled stand against negative-sum games. I found out about the Prisoner's Dilemma pretty early in life, but not at the age of seven. I'd refused simply because I didn't want to get hurt, and standing in the corner was an acceptable price to pay for not getting hurt.
More importantly, I realized that I had always known this—that the real memory had always been lurking in a corner of my mind, my mental eye glancing at it for a fraction of a second and then looking away.
In my very first step along the Way, I caught the feeling—generalized over the subjective experience—and said, "So that's what it feels like to shove an unwanted truth into the corner of my mind! Now I'm going to notice every time I do that, and clean out all my corners!"
This discipline I named singlethink, after Orwell's doublethink. In doublethink, you forget, and then forget you have forgotten. In singlethink, you notice you are forgetting, and then you remember. You hold only a single non-contradictory thought in your mind at once.
"Singlethink" was the first new rationalist skill I created, which I had not read about in books. I doubt that it is original in the sense of academic priority, but this is thankfully not required.
Oh, and my fifteen-year-old self liked to name things.
The terrifying depths of the confirmation bias go on and on. Not forever, for the brain is of finite complexity, but long enough that it feels like forever. You keep on discovering (or reading about) new mechanisms by which your brain shoves things out of the way.
But my young self swept out quite a few corners with that first broom.