Chasing the dream....or just dreaming?

An interview with a storeowner in the front of the Lonely Planet "NYC" describes the city as a place where "you feel that your dreams are just around the corner...that anything is possible" (paraphrased). That's an optimisitic thought, but also, I think, a scary one: how do you know if you're just chasing a will-o-the-wisp? You could end up old and feeble and still thinking your dream is "just around the corner," when really you've spent your whole life following a path you thought would take you there and instead led you down into a gully full of a lot of brambles and mosquitoes, but no dream.