I think worrying is in part a habit and in part anxiety. I can have some anxiety and still not worry about what the future brings (I do worry about the present, e.g. "do these people like me?"). I do not worry a lot because I have said to myself for a long time that it's just not worth the energy and time that is spent on it. If you realize how, and really believe that worrying is useless I think it should be possible and not too difficult to quit. Then again maybe it was just not so difficult for me and I'm just not the kind of person who worries a lot. My life is much better since I stopped worrying. I can't seem to shake off the anxiety or paranoia though.