My knowledge of the human psyche is as yet imperfect. Certain areas won't yield to computation.

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

He had seen too much of the cosmos to have any great faith in man's ability to understand it.

So much American science fiction is parochial - not as true now as it was years ago, but the assumption is one culture in the future, more or less like ours, and with the same ideals, the same notions of how to do things, just bigger and flashier technology. Well, you know darn well it doesn't work that way.

I have yet to see any problem, however complicated, which, when you looked at it in the right way, did not become still more complicated.

What five books would I like to be remembered for? Well... Tau Zero, I like that one especially. It was somewhat of a tour de force, and I think it got across what I was trying for.

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