Only one who devotes himself to a cause with his whole strength and soul can be a true master. For this reason mastery demands all of a person.

I learned many years ago never to waste time trying to convince my colleagues.

The mind that opens to a new idea never returns to its original size

Concepts which have proved useful for ordering things easily assume so great an authority over us, that we forget their terrestrial origin and accept them as unalterable facts. They then become labeled as 'conceptual necessities,' etc. The road of scientific progress is frequently blocked for long periods by such errors.

One picture is worth a thousand words

When the nazis came to power, I looked to the universities that prided themselves upon their intellectual freedom, and they failed me. I looked to the German press, which prided itself on the freedom of the press, and it failed me. Until at last the churches stood alone, and that for which I once had little regard earned my respect.

Out yonder there is this huge world, which exists independently of us human beings and which stands before us like a great, eternal riddle, at least partially accessible to our inspection and thinking