The word "yoga" literally means "uniting", because when you're doing it you are uniting your mind and your body. You can tell this almost immediately because your mind will be thinking, "Ouch, that hurts," and your body will say, "I know." And your mind will think, "You have to get out of this position." And your body will say, "I agree with you, but I can't right now. I think I'm stuck.