Steve Jobs, via BoingBoing says:

My third story is about death. When I was 17 I read a quote that went something like “If you live each day as if it was your last, someday you’ll most certainly be right.” It made an impression on me, and since then, for the past 33 years, I have looked in the mirror every morning and asked myself, “If today were the last day of my life, would I want to do what I am about to do today?” And whenever the answer has been “no” for too many days in a row, I know I need to change something. Remembering that I’ll be dead soon is the most important thing I’ve ever encountered to help me make the big choices in life, because almost everything–all external expectations, all pride, all fear of embarrassment or failure–these things just fall away in the face of death, leaving only what is truly important. Remembering that you are going to die is the best way I know to avoid the trap of thinking you have something to lose. You are already naked. There is no reason not to follow your heart.