Like the points of a compass, the knowledge essential for success, health, and happiness comes is fours.  Each of these "crosses" is important; none can be skipped without paying a price.  The cross that you start with will be the one that most directly addresses your strongest unmet need.  However, just as "all roads lead to Rome", all crosses lead to The Cross of Wisdom.  The four points of this cross - Know Yourself, Know Your Purpose, Know Your World, and Know Your God - form the foundation on which all the other crosses are built.