If you’re looking to create a timeless sense of purpose and to shape the overall mission of your life, then you should use principles. Establishing a set of principles creates a compass to which you can refer whenever something is in doubt or you need to take a stand or evaluate any particular opportunity, behavior, or situation.
"Paying rapt attention, whether to a trout stream or a novel, a do-it-yourself project or a prayer, increases your capacity for concentration, expands your inner boundaries, and lifts your spirits, but more important, it simply makes you feel that life is worth living." (Winifred Gallagher, Rapt)
Once you've found something you're excessively interested in, the next step is to learn enough about it to get you to one of the frontiers of knowledge. Knowledge expands fractally, and from a distance its edges look smooth, but once you learn enough to get close to one, they turn out to be full of gaps.