To introduce something altogether new would mean to begin all over, to become ignorant again, and to run the old, old risk of failing to learn.

I'm not a speed reader. I'm a speed understander.

Emotionally I am an atheist. I don't have the evidence to prove that God doesn't exist, but I so strongly suspect he doesn't that I don't want to waste my time.

There is no merit to discipline under ideal circumstances. I must have it in the face of death or it is worthless.

A fire-eater must eat fire even if he has to kindle it himself.

Before another century is done it will be hard for people to imagine a time when humanity was confined to one world, and it will seem to them incredible that there was ever anybody who doubted the value of space and wanted to turn his or her back on the Universe.

The energy requirements for interstellar travel are so great that it is inconceivable to me that any creatures piloting their ships across the vast depths of space would do so only in order to play games with us over a period of decades. If they want to make contact, they would make contact; if not, they would save their energy and go elsewhere.