If there is one question that can change your life, it will probably be whether you are passionate about whatever you are doing in life.  Steve Jobs sums it up real nicely in this short video.  People who succeed are those who are passionate in what they are doing.  Why else would they be able to keep doing things at their peak level on a sustained basis?  And therein lies the secret of success.

As he also sums up nicely in this quote:

"For the past 33 years, I have looked in the mirror every morning and asked myself: "If today were the last day of my life, would I want to do what I am about to do today?" And whenever the answer has been "No" for too many days in a row, I know I need to change something..almost everything - all external expectations, all pride, ...