Grey's Anatomy, Season 5

Meredith:
[voiceover] Practicing medicine doesn't lend itself well to the making of friends. Maybe because life and mortality are in our faces all the time. Maybe because in staring down death everyday, we're forced to know that life, every minute, is borrowed time. And each person we let ourselves care about is just one more loss somewhere down the line. For this reason, I know some doctors who just don't bother making friends at all. But the rest of us, we make it our job to move that line. To push each loss as far away as we can.