The truth of a theory is in your mind, not in your eyes.

In one's youth every person and every event appear to be unique. With age one becomes much more aware that similar events recur. Later on, one is less often delighted or surprised, but also less disappointed than in earlier years.

In the middle of every difficulty lies opportunity.

The only sure way to avoid making mistakes is to have no new ideas.

By an application of the theory of relativity to the taste of readers, today in Germany I am called a German man of science, and in England I am represented as a Swiss Jew. If I come to be represented as a bête noire, the descriptions will be reversed, and I shall become a Swiss Jew for the Germans and a German man of science for the English!

It is really a puzzle what drives one to take one's work so devilishly seriously.

There is, however, one other human right which is infrequently mentioned but which seems to be destined to become very important: this is the right, or the duty, of the individual to abstain from cooperating in activities which he considers wrong or pernicious.