As soon as we have contrived to give our pupil an idea of the word "Useful," we have got an additional means of controlling him, for this word makes a great impression on him, provided that its meaning for him is a meaning relative to his own age, and provided he clearly sees its relation to his own well-being. This word makes no impression on your scholars because you have taken no pains to give it a meaning they can understand, and because other people always undertake to supply their needs so that they never require to think for themselves, and do not know what utility is. "What is the use of that?"

Emile, or On Education (1762) - Book III