"Sapiens: A Brief History of Humankind" by Yuval Noah Harari. Hands down the book that most influenced me. The book had (for me) not one but several simple-yet-profound ideas that were forever inserted into the foreground of how I make sense of the world. For example, the existence of shared myths that allow humans to cooperate on a large scale. Or how I too, am religious, though I was sure I wasn't. Can't recommend…
For example, I never thought about how ideas that are touted by organizations or religions are frequently argued to be "natural" or "divine" or somehow sewn into the fabric of the universe. The book helped me to become a little more skeptical by portraying how versatile and diverse human societies can be, and how there is truly very little that is "natural", "eternal", and meant to be.
Similarly, the book helped me to realize how unprecedented the current rates of economic and technological growth are. Its an exciting time to be alive, filled with almost infinite possibilities, and that fact is especially inspiring when you understand how much more restrictive previous generations and cultures were.