And Germans by and large put the coins back. They just use a Euro coin to help with that social institution. Most people could totally afford to lose a Euro, but it's The Right Thing to do to bring the cart back.

Similar to how when you are working as a programmer, it's good for not to break 'master'. You could rely completely on an honour system, or you could have an automated merge-check. In most places, the merge-check can be arbitrarily easy to bypass, but programmers would still by and large abide it.