The Growth Mindset.<p>It just conveys a simple theory and if you keep it in the back of your mind, you won't be easily defeated when learning anything new.
How to win friends and influence people - It's mentioned here all the time but I think it would have helped get over some of my social anxiety in high school. Maybe this is particular to me but I get the sense that American society doesn't teach kids how to interact with others.
10 years ago - The Gulag Archipelago (Abridged) or One Day in the Life of Ivan Denisovich : Solzhenitsyn<p>20 years ago - Meditations : Marcus Aurelius<p>30 years ago - Zen Flesh Zen Bones : Paul Reps<p>Any time: Anything by: Robert Sapolsky, John Gottman, Early Jonathan Lethem novels, Peter Clines, Margaret Atwood
Maps of Meaning by Jordan Peterson. I've gone through several core belief changes in my life (religious, philosophical, interpersonal) and the book would have helped me understand what I was going through.