We don't get to know people when they come to us; we must go to them to find out what they are like.

Without my attempts in natural science, I should never have learned to know mankind such as it is. In nothing else can we so closely approach pure contemplation and thought, so closely observe the errors of the senses and of the understanding, the weak and strong points of character.

All theory, my friend, is grey, But green is life's glad golden tree.

What matters in art is not thinking but making.

The experiences show us just as we are; they make us see our own defects.

Our mistakes and failures are always the first to strike us, and outweigh in our imagination what we have accomplished and attained.

Should I not be proud, when for twenty years I have had to admit to myself that the great Newton and all the mathematicians and noble calculators along with him were involved in a decisive error with respect to the doctrine of color, and that I among millions was the only one who knew what was right in this great subject of nature?