My answer to How did you find out the career you were passionate about?
Answer by Ken Larson:
By examining our value system.
Our existence and our mental universe are driven by factors that we as individuals inherit through the gene pool, as enhanced by our experiences in life.
In short we are most at peace when we are in sync with the personal value system that has evolved as a result of the above factors and when we are permitted to pursue our values in our personal and professional endeavors.
If we cannot achieve that harmony we will seek change. Human beings must seek a purposeful life in their value system. It is waiting there for them.