One of the best books I have ever read.
Do you feel that you don't really have the passion for your work?
If you have passion then maybe you feel that you don't have any particular mission?
Long story short this book will liberate you.
Your gain your passion with work and effort you put into something you do - preferably that pays your bills. If you like something or you have no other choice and you have to do something you still can make it your passion. In my opinion, that's liberating. What's the alternative? For me, I would need to be sad that I can't make reading fantasy books my job...
After watching Brett Victor Inventing on Principle, I was thinking about my mission... What should it be? Cal Newport puts that into another perspective. First you have to gain expert experience and skills to have a mission. With enough knowledge in your field, it will be obvious next step to do. Keep build your skills and mission will show up eventually.
The most important idea from the book: Deliberate Practice.
Find something hard in your field and try to understand it. For me, it's learning more algorithms and languages out of my comfort zone. For now I've decided to read "How To Design Programs" but I want to learn a language with static typing after I go back from holiday.
Cons: some of the xamples are really extreme and book is really repetitive - I don't mind it as I treat it as a chance to better learn the ideas, but it's easy to find commenters annoyed by it so it's worth to mention.