"Twenty years from now you will be more disappointed by the things that you didn’t do than by the ones you did so. So throw off the bowlines. Sail away from the safe harbor. Catch the trade winds in your sails. Explore. Dream. Discover."

Often attributed to Mark Twain, but there's no proof he ever said it. To me it sounds more like Hemingway or someone along those lines. Still, a great quote, and a great motto in life.