Whats up with this Half-Full, Half-Empty thing?

I've always been wondering about this half-full, half-empty thing. I think its more of a way that you think about it. If you think about it when your pouring water into a cup, and you stop at the half, you say half-full. When your drinking the water, and you finish half, you say its half-empty. Makes things seem like it makes more sense. All about how you think about it.