child: why do they sell board games in bookstores
loving parent: because there's a manual in every board game
child: why don't they sell cars in bookstores
loving parent: because when you're buying a board game, what you're really buying is the rules, and those are in the manual. a car manual with no car can't drive you, but if you have the manual to a board game you could play it without the pieces. there are people who can play a game of chess just by saying where they're moving the pieces and imagining the board, but it's very hard so they give you a board and pieces to help you.
loving parent: That's why you never see Mousetrap in bookstores. Because you can't play it with just the manual.
moral: kids these days don't know about Mousetrap