"Always be learning. The world is constantly changing, and you need to keep up."
The more you struggle to live， the less you live.
The preservation of the means of knowledge among the lowest ranks is of more importance to the public than all the property of all the rich men in the country.
Forests teach us patience—growth takes time, but the rewards are everlasting.
No man, for any considerable period, can wear one face to himself and another to the multitude, without finally getting bewildered as to which may be the true.
The scientific study of behavior must be based on objective, measurable data.