I'm not sure if I live by any quotes, but there are a few that have impacted me in one way or another.
For example, while I joined the Army for many reasons, and any of a hundred movies and commericals left their mark, the phrase "Be all you can be in the Army" probably did more to make me raise my hand than the rest. At the heart of it all, it wasn't boredom or patriotism or a coin toss that really made me do it, I wanted to know if I COULD do it.
In the end, I did learn that I was capable of doing it. I learned that almost every limit I had ever taken note of was simply mental. I learned that even when three of your four limbs are pinned in a fight, you still have not lost. I learned that no matter how exhausted I was, no matter how miserable, so long as I was still breathing I could keep moving forward. This was a trivial lesson in retrospect and it probably is obvious to anybody who has played any sport seriously.
The most important lesson I learned was that no matter how hard you work, no matter how much you struggle, in the end victory or defeat often lies in matters outside of your control. It was at this moment, when everything I had ever believed in turned out to, at best, be a warped version of reality, that I read the book Fight Club by Chuck Palahniuk and came across a quote that somehow made sense of it all: "A minute of perfection was worth the effort. A moment was the most you could ever expect from perfection."