I've always found the idea of living each day[1] as though it were my last to be odd. If I knew that a day was going to be my last, there are potentially fun or useful activities to choose from which carry a very high risk. That day would be the day to do things that have a significant chance of killing you any time you do them... and by "significant", I mean greater than five percent, say, not things like skydiving.

[1] Some versions of this idea use hour, and I've heard someone say "second". How do you live each second as if it were your last? No one who does this would last long; there's no point in doing most of what we do if we're going to die in the next second, right? But maybe people who say "hour" or "second" are just betraying that they don't really mean it.