The writer must earn money in order to be able to live and to write, but he must by no means live and write for the purpose of making money.Karl Marx
The product of mental labor - science - always stands far below its value, because the labor-time necessary to reproduce it has no relation at all to the labor-time required for its original production.Karl Marx
A man is relieved and gay when he has put his heart into his work and done his best; but what he has said or done otherwise shall give him no peace.Ralph Waldo Emerson
A man builds a fine house; and now he has a master, and a task for life: he is to furnish, watch, show it, and keep it in repair, the rest of his days.Ralph Waldo Emerson
If a man walks in the woods for love of them half of each day, he is in danger of being regarded as a loafer. But if he spends his days as a speculator, shearing off those woods and making the earth bald before her time, he is deemed an industrious and enterprising citizen.Henry David Thoreau