The greatest obstacle to being heroic is the doubt whether one may not be going to prove one's self a fool; the truest heroism is to resist the doubt, and the profoundest wisdom to know when it ought to be resisted, and when it be obeyed.

A life without examination is not worth living.

We shall not cease from exploration, and the end of all our exploring will be to arrive where we started and know the place for the first time.

I don't believe in diversification. I prefer to concentrate on a few good ideas.