Only a life lived for others is a life worthwhile.
If the bees disappear, man would have only four years of life left.
If you cannot explain it simply, you do not understand it enough.
Outer changes always begin with an inner change of attitude.
The supreme goal of all theory is to make the irreducible basic elements as simple and as few as possible without having to surrender the adequate representation of a simple datum of experience.
One should guard against preaching to young people success in the customary form as the main aim in life. The most important motive for work in school and in life is pleasure in work, pleasure in its result, and the knowledge of the value of the result to the community.