I actually have two favorite quotes and they really go hand in hand.
"The only mistake in life is the lesson not learned." - Albert Einstein
"You can never make the same mistake twice. The second time you make it, it's no longer a mistake, it is a choice." - Lauren Conrad
I look at these both as a reminder that every lesson, mistake, event, etc. should be looked at as a choice. A choice to either learn from something, experience something, or determine who and what we are. And from that, we then make a choice to either continue on a path (a good or bad one) or forge a new one with the knowledge we now have. Everything we do really comes down to the choices we make.