A man is not idle, because he is absorbed in thought. There is a visible labour and there is an invisible… — Victor Hugo

A man is not idle, because he is absorbed in thought. There is a visible labour and there is an invisible labour.

In the original (French)

On n’est pas inoccupé parce qu’on est absorbé. Il y a le labeur visible et le labeur invisible.

Source: Wikiquote · CC BY-SA 4.0