"Andrew Carnegie (1835 -1919) began as a bobbin boy in a textile mill in Pennsylvania. He became rich by working his way up the iron and steel business in order to build railroads. He understood very early that the industrial revolution was going to change everything in America. He was quick to recognize that steel was a better product than iron and invested in steel. He put his steel company to work building railroads and then as the railroad expansion was coming to an end he started promoting and selling steel beams for city skyscrapers. In today's dollars, Carnegie was worth just shy of $300 billion."
What I love about this story is a subtle point at the end. When his existing market "was coming to an end" he changed it, and continued his success. Understand where you are, but always look forward.