Essentialism is a book that has completely changed my outlook on productivity and business.
Only doing the things that will have the highest return. I'm someone who loves to have a multitude of different things on my plate - this was causing me to plateau and not reach altitudes I was capable of if only I was willing to focus in on what is most important.
This is a must read for anyone that wants to be better at time management, productivity, and have higher returns on their time investments.