The answer is derived from the quotable quote from Adam Smith in The Wealth of Nations is: "It is not from the benevolence of the butcher, the brewer, or the baker that we expect our dinner, but from their regard to their own interest."
In other words, the butcher isn't trying to be a nice guy, he's trying to earn income for himself. Most people who work the cash register in any fast food chains aren't doing it because they love hamburgers or because they love customers. They're doing it because they need a job and to be certain of that working will develop their situation in life and maybe one day this will help them to reach their goals.
