Cal Newport's latest book is So Good They Can't Ignore You. In the book he makes the case for adopting what he calls the 'craftsman mindset' over the 'passion mindset' in developing a fulfilling a career. Find out what you are good, work hard at becoming an expert in that discipline and you will find success. Spending hours looking inside yourself for your true purpose and passion, will only lead to frustration. He makes a compelling case. You can find his excellent blog here.