The worthwhile problems are the ones you can really solve or help solve, the ones you can really contribute something to... No problem is too small or too trivial if we can really do something about it.

While I am describing to you how Nature works, you won't understand why Nature works that way. But you see, nobody understands that.

My rule is, when you are unhappy, think about it. But when you're happy, don't. Why spoil it? You're probably happy for some ridiculous reason and you'd just spoil it to know it.

We have found it of paramount importance that in order to progress, we must recognize our ignorance and leave room for doubt.

You should not fool the laymen when you're talking as a scientist... . I'm talking about a specific, extra type of integrity that is not lying, but bending over backwards to show how you're maybe wrong, [an integrity] that you ought to have when acting as a scientist. And this is our responsibility as scientists, certainly to other scientists, and I think to laymen.

There is no authority who decides what is a good idea.

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.