Four Thousand Weeks: Time Management for Mortals
This book has had a lasting impact on me. The gist of the book is that time is finite, and our efforts to "do it all" are futile. There is literally not enough time to do it all, and acknowledging that fact can be extremely liberating. This book forced me to rethink my attempts at maximizing productivity, and helped refocus on the things and relationships that are most important in my life. I'd highly recommend this read.