One secret to maintaining a thriving business is recognizing when it needs a fundamental change. 50 Harvard Business Review | December 2008 | hbr.org Business Reinventing Y our by Mark W. Johnson, Clayton M. Christensen, and Henning Kagermann Model IN 2003, APPLE INTRODUCED THE IPOD WITH THE ITUNES STORE, Jim Frazier revolutionizing portable entertainment, creating a new market, and transforming the company. In just three years, the iPod/iTunes combination became…