he would now have comprehended that work consists of whatever a body is obliged to do, and that play consists of whaterver a body is not obliged to do. And this would help him to understand why construcing artificial flowers or performing on a tread-mill, is work, whilst rolling nine-pins or climbing Mont Blanc is only amusement. There are wealthy gentlemen in England who drive four-horse passenger-coaches twenty or thirty miles on a daily line, in the summer, because the privilege costs them considerable money; but if they were offered wages for the service that would turn it into work, then they would resign.
Mark Twain, The Adventures of Tom Sawyer
human-nature