Differences

Why is it that men say they don't want a girl who will jump in bed with them on the first date, but when the girl doesn't put out at the end of the night, they're out of there faster than a speeding bullet? Why are we always seeking a challenge? I understand that it's human nature to want something until you have it, but if this is how we are, how do people ever end up getting married? Do they just get tired of the game or is it like being a football player and there comes a time when you are forced to retire? How are you supposed to show interest in someone while still playing hard to get?