The more you know, the more you realize what you don't know.
I remember way back in grade school, and we had a person come in and give us a lecture on philosophy. Well, the way he described it was with a circle. Inside the circle was everything that we know, while the edge of the circle was the beginning of what we don't. As we learn more, the circle gets bigger, but then again, so does the circumference, meaning that the more we know, the more we actually don't know. But, he said that was a good reason to keep learning more, so that our circles would get bigger, but also the realization that there is always more to learn.