Never ending questions in science

Via RealClimate.org, this great quote by Earl C. Kelley from a 1951 learning workshop:

We have not succeeded in answering all our problems. The answers we have found only serve to raise a whole set of new questions. In some ways we feel we are as confused as ever, but we believe we are confused on a higher level and about more important things.

It's one of the best expressions of "productive ignorance", the notion that no matter how hard we try, we will never truly discover everything there is to know about the universe. This sense of doubt and uncertainty is not a bad thing—it's precisely the thing makes science fun.