This quote is from Cyteen, by C.J. Cherryh.
A brief glossary:
sets: Psychological and informational building blocks. These characters live in a world where applied child psychology is a hard science. Deep-sets are the deepest knowledge/belief about how the world works; value-sets are one's conceptions of good and bad, et cetera.
azi: Artificially-educated ("tape-raised") humans, who get not only their school-learning, but also most of their entire rearing, from cleverly programmed audio, video, etc. training.
Alpha: The highest intelligence rating an azi can have.
Gamma: A lower azi intelligence rating, by no means stupid but not inclined to excess introspection.
Tester: An azi whose occupation is to do practical tests on tape programs intended for other azi.
CIT: A traditionally raised human, who only takes tape for school or as a result of psychological problems.
eetee: Alien to the local common modes of thought in a way that lessens meaningful conversation; psychologically weird; disconnected from reality. Slang.
He said sometimes when you're young you have to think about things, because you're forming your value-sets and you keep coming up with Data Insufficient and finding holes in your programs. So you keep trying to do a fix on your sets. And the more powerful your mind is and the more intense your concentration is, the worse damage you can do to yourself, which is why, Justin says, Alphas always have trouble and some of them go way off and out-there, and why almost all Alphas are eccentric. But he says the best thing you can do if you're too bright for your own good is what the Testers do, be aware where you got which idea, keep a tab on everything, know how your ideas link up with each other and with your deep-sets and value-sets, so when you're forty or fifty or a hundred forty and you find something that doesn't work, you can still find all the threads and pull them.
But that's not real easy unless you know what your value-sets are, and most CITs don't. CITs have a trouble with not wanting to know that kind of thing. Because some of them are real eetee once you get to thinking about how they link. Especially about sex and ego-nets.
Justin says inflexibility is a trap and most Alpha types are inward-turned because they process so fast they're gone and thinking before a Gamma gets a sentence out. Then they get in the habit of thinking they thought of everything, but they don't remember everything stems from input. You may have a new idea, but it stems from input somebody gave you, and that could be wrong or your senses could have been lying to you. He says it can be an equipment-quality problem or a program-quality problem, but once an Alpha takes a falsehood for true, it's a personal problem.
This was important for me because I was about fifteen when I read this book for the first time, and dealing firsthand with the problems of being too smart for my own good and undersocialized. I started trying to trace back where I got some of my weird ideas from, and became at least marginally more aware of what I was putting in my head. While it did not solve all my problems, it provided a good solid basis to start from, and was very helpful as a common set of vocabulary when iroshi started me rewiring my brain into something functional, thank-you-very-much, after the mess of it that was left in the aftermaths of Shawn and BJ.