Imagine if just some of those planets contained the right conditions for life and some of those had life. While not a believing in the UFO/alien abduction nonsense, I do wholeheartedly believe that there is life in the universe - it's simply too vast for there not to be. If, on the other hand, we are the only living things in this great big mess, then it is the most tragic thing ever and something worth weeping over.
Now, if you really want to feel insignificant, hit the jump.
Okay, so you see that tiny little speck on the brown band of light on the right hand side of the picture, the dead pixel looking thing? Yeah, that's Earth as seen from 3.7 billion miles away. This picture is famously called Pale Blue Dot and was taken by Voyager 1 in 1990 as the spacecraft reach the end of the solar system. According to Wikipedia, Carl Sagan himself asked NASA to take the picture before they powered downed Voyager's camera.
It's pretty humbling to see that picture and know that despite what we may think, we're nothing more than a speck in the larger universe.