This is embarrassing. I grew up with sorta fundie parents (they got better) and dropped out of school early (religious schools...), so it might be different for HNers that had a solid mental upbringing.<p>A Brief History of Time because it pretty much slapped any thoughts I had of a supernatural universe/god right out of my mind. I know it's not highly regarded, but for a rather ignorant guy, it woke me up.<p>The Selfish Gene (inc The Extended Phenotype). This is one I think is the most powerful, even for people that had OK education. Showing how life could possibly evolve, just with random mutations and non-random survival made it real to me that we live in a natural world. And not just that, but that since it's so obviously a natural world, it's up to us to decide what is right, what our purpose is. The earth and nature aren't going to help us there - it's <i>our</i> call, full stop. That is huge, and many otherwise seemingly well educated people don't seem to get it.<p>Heuristics and Biases. (Though Thinking Fast and Slow might be more approachable.) This book opened me up to the fact that I'm running on busted hardware. That I've got serious, unfixable, biases built into my brain. That a lot of what I do is a fast but inaccurate parallel system at work. (Interestingly, this is the essence of Taoism, wu wei).<p>Lately, LessWrong. (Available as a book called Rationality: From AI to Zombies). These sequences have helped me, well, get less wrong, slowly, at making decisions and general thinking. I try to be aware of when I'm being biased and incorrect. I make better predictions and actively try to update my priors, instead of just confirming my previous beliefs. As I get older (34) I find I'm unwittingly acting close minded on occasion, and need to actively work against it.