Science is uncertain.

No one really understands quantum mechanics.

You see, I get such fun out of thinking that I don't want to destroy this most pleasant machine that makes life such a big kick.

The unanswerable mysteries... the attitude that all is uncertain... to summarize it - the humility of the intellect.

Only realistic flight schedules should be proposed, schedules that have a reasonable chance of being met. If in this way the government would not support them, then so be it. NASA owes it to the citizens from whom it asks support to be frank, honest, and informative.

I don't have to be good because they think I'm going to be good.

People may come along and argue philosophically that they like one better than another; but we have learned from much experience that all philosophical intuitions about what nature is going to do fail.