Why some people play 'Hard to get' with those who love them.

I have a question to ask you guys and gals. Actually this should have been posted long back when the Valentine's day was around. Some girls and guys when they understand that somebody likes them will immediately start playing 'Hard to get' with that person and start acting un-interested even if they are equally interested. Unfortunately this sometimes back fires and the other person who wants to propose you will think that you are not interested and will ignore you.

So why do some males and females play this 'Hard to get' game with those who like them? Are they trying to appease their egos? Would you play 'Hard to get' with somebody who likes you and wants to propose you?