The more sobering of two notions
Thinking of ourselves in relation to the the known universe, makes us realize how small we are in the grand scheme of things. Our planet represents one speck on a grain of sand on the world's biggest beach. And we are a speck on that speck. Putting it in perspective like that can make us worry less about the little annoyances that life sometime throws our way.
But the far more shattering notion is to think of where we stand in the flow of time. With time stretching back into an infinite past, and stretching forward into the infinite future (practically speaking - although Stephen Hawking would dispute it) we occupy only the barest fraction of the smallest moment of that time-line. To me, thinking this way makes me realise just how precious our lifetimes are. They are momentary moments only. Do what you love - love what you do - live with passion