Surely you've heard the expression live every day as though it were your last, or some variation. The meaning is something to the effect of spend your time on Earth in the best ways you can, which I think is a nice thought. But, like most warm and fuzzy expressions, it should not be taken literally.

Suppose you could know with certainty that a day would be your last. Do you really think that you should behave the way you would on that day, everyday? Some people would panic and rush around in an attempt to get their affairs in order. Others would repent all their percieved wrongdoings to their diety of choice. Still others would engage in hedonistic, risky behaviour without fear of negative consequences. Now imagine this on a global scale--a planet full of religious fanatics and drug-fueled sex addicts. Day after day. All because we took some silly expression at face value.

Hey, that's not half-bad.