Why do guys play hard to get?

Why do guys play hard to get? One day they act like the like you and the next day they act like your not that important? How do you know if they really do like you or not? Or do they just want something?

A guys world works different each day, when alone most guys will get on real well with girls. But when they are in public or with friends, they'll act all weird, a sort of form of paranoia. The way guys act with a girl when alone is normally the true way he feels.

okay thanks a lot =]