Randy Pausch, a professor at Carnegie Mellon, found out that he had pancreatic cancer and had only 3-6 months to live. And he delivered his now-famous Last Lecture. This is an uplifting (yes, uplifting!) lecture on the dreams he had and the path he took in achieving those dreams.
If you haven't heard his lecture yet, take an hour to do so. It's widely available on youtube.
Prof. Randy passed away yesterday, bless-his-soul, at the age of 47. His inspiring lecture has been made into book as well, for those who prefer to read rather than watch.
Back to the original question, though. Most of us don't live our fullest until we know we don't have time anymore. I myself is included. And of course, it's easy to say that we will aim for this, but how exactly do we plan to live to the fullest?