I want to share what I read from *The Upside of Irrationality* to a friend who doesn't understand English very well. Here is the context of where this phrase comes from (though I think this phrase is self-explainatory, but I decide to give the context just in case) :

> 
> This is also why playing hard to get can be a successful strategy in
>  the game of love. If you put an obstacle in the way of someone you
>  like and [he or she] keeps on working at it, you're bound to make that
>  person value you even more.
> 
> 
>