There is no harm in doubt and skepticism, for it is through these that new discoveries are made.

The worthwhile problems are the ones you can really solve or help solve, the ones you can really contribute something to.

You can know the name of a bird in all the languages of the world, but when you're finished, you'll know absolutely nothing whatever about the bird... So let's look at the bird and see what it's doing -- that's what counts. I learned very early the difference between knowing the name of something and knowing something.