What one has wished for in youth, in old age one has in abundance.

Theories are usually the over-hasty efforts of an impatient understanding that would gladly be rid of phenomena, and so puts in their place pictures, notions, nay, often mere words.

Thou must (in commanding and winning, or serving and losing, suffering or triumphing) be either anvil or hammer.

It is so hard that one cannot really have confidence in doctors and yet cannot do without them.

As soon as any one belongs to a narrow creed in science, every unprejudiced and true perception is gone.

What is hardest of all? That which seems most simple: to see with your eyes what is before your eyes.

Always to distrust is an error, as well as always to trust.