Part of the beauty and awe I get whenever I reread that famous excerpt from Carl Sagan's Pale Blue Dot is the sense of how ephemeral and delicate our existence, and even the very human concept of "existence", is. We are infinitesimally small and yet, through no fault of our own, our days, how we fill them, and the people we know hold some measure of importance to us. And it will all be gone - eventually. It's a very somber note yet it makes me feel a certain sense of peace.
"Look again at that dot. That's here. That's home. That's us. On it everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives. The aggregate of our joy and suffering, thousands of confident religions, ideologies, and economic doctrines, every hunter and forager, every hero and coward, every creator and destroyer of civilization, every king and peasant, every young couple in love, every mother and father, hopeful child, inventor and explorer, every teacher of morals, every corrupt politician, every 'superstar,' every 'supreme leader,' every saint and sinner in the history of our species lived there--on a mote of dust suspended in a sunbeam."