Not that we would ever imply that you won't be taught everything you need to know about the mysteries of dating by the He's Just Not That Into You movie (even though it made the Observer's Sara Vilkomerson "not want to be a member of the entire human race"), but a new study has shown that a woman should indeed play hard to get unless she wants to end up a lonely spinster, cursing the day she decided not to buy a copy of The Rules.