W. B. Yeats The Second Coming
The best lack all conviction, while the worst / Are full of passionate intensity.
This is one you really start to notice around you as you think about it. As time has gone on, I often wondered if/why I would sometimes feel as if I was losing [what seemed like] my competitive spirit the more I seemed to accomplish. I began to feel more and more giving in nature, not just with my kids (people often attribute a change in heart to having children), but with everyone. This line from The Second Coming, especially taken by itself, does a very nice job of summarizing it.