John Maxwell is famous for this statement, probably the defining sentence of his writing and speaking career.  Having been involved with leadership and leadership training at some level for nearly 20 years, I have really dialed into the statement as the key way to catalyze, initiate and impart lessons of leadership.  It's one of those sentences that contain a world of instruction, content and insight.  It's the key that starts my leadership engine, and precipice over which other leadership thoughts flow.