If we are told that we must not have a thing, we want it more than ever. And if we are told not to do a thing, we feel impelled to do it.
A schoolboy once came upon a form-mate smoking in a quiet corner behind the gymnasium.
‘Are you enjoying it, Jenkins?’ he asked.
‘Not very much,’ admitted Jenkins, ‘but the ban on smoking makes it more exciting.’
The proverb derives, of course, from the story of Adam and Eve.