A fanatic is a man who, when he's lost sight of his purpose, redoubles his effort.

I wrote the first book, Harvest of Stars, and as I was writing it, I saw that certain implications had barely been touched on... It's perfectly obvious that two completely revolutionary things are going on, with cybernetics, and biological science.

Give fear no hold on you. Keep sinews loose and senses open, ready at every instant to flow with the rush of action.

Happier are all men than the dwellers in Faerie – or the gods, for that matter…Better a life like a falling star, bright across the dark, than a deathlessness that can see naught above or beyond itself…the day draws nigh when Faerie shall fade, the Erlking himself shrink to a woodland sprite and then to nothing, and the gods go under. And the worst of it is, I cannot believe it wrong that the immortals will not live forever.

A fanatic's willingness to kill or be killed in the service of a cause cannot prove the rightness of that cause.

If we knew exactly what to expect throughout the Solar System, we would have no reason to explore it.

We live with our archetypes, but can we live in them?