One book is too restrictive to decide. People change, surroundings change, situations change...so would it be with books that have changed us or influenced us.

One book is too restrictive to decide. People change, surroundings change, situations change...so would it be with books that have changed us or influenced us. I'll leave you here not with a book, but with one tiny piece of one tiny book: The first chapter of "Illusions" by Richard Bach. As with other fantastic works that others have listed here, a distinguishing factor about these impactful or "life changing" works is that you can re-read them countless times and benefit from them anew on every read. This first chapter is one such work for me. I'm not implying that the rest of "Illusions" is worse than this first chapter (on the contrary, it's great), but this chapter is short, yet so powerful, and best of all, it stands by itself. Bonus, if you like to read brief but powerful pieces, pick up "The Prophet" by Kahlil Gibran and read the chapters that interest you. I'd suggest the "On Giving" chapter as a great start.