Grey's Anatomy, Season 3

Meredith:
[voiceover] First do no harm, easier said than done. We can take all the oaths in the world, but the fact is, most of us do harm all the time. Sometimes even when we're trying to help, we do more harm than good. And then the guilt rears its ugly head. What you do with that guilt is up to you. We're left with a choice. Either let the guilt throw you back into the behavior that got you into trouble in the first place, or learn from the guilt and do your best to move on.