"Life is Short."

I hate this quote with a passion. Why do people say it? Personally, I think a life expectancy of 78 years (in the US) is a damn long time.
When I hear people say this, I just want to smack them. I am always tempted to ask what they have experienced that is longer than life, since it is so short. They sound so stupid.
I get that life is short in comparison to time itself, but that isn't usually the reference they are making. Many people say that as an excuse to do something stupid or unusual. So the context is completely wrong.