The 7 Habits of Highly Effective People (Steven R. Covey)
In short: this book can change your life, or at least make you think hard about it.
It’s not just about how to become effective or productive, it’s about how to train your character so that you live in harmony with yourself.
Honestly speaking, I’ve been reading this book for about a year. Making pauses for weeks, returning back and rethinking. It just contains so much information and inspiration that I had to stop and think about all I have read, to adopt it, even to have a rest.
It’s very difficult to apply all the principles described there and I’m sure it’s not even necessary. Everybody takes what he or she need. But once taken, you never regret.