Often, when our mind takes over, our ego has taken control, the ego likes to criticize us, telling us what we should or shouldn't do. This can distort one's reality and we can quite easily wind ourselves up over nothing.
Practicing presence is vital for a peaceful existence. When you are concentrating only on the present moment you are more able to act as an observer to your ego and decide not to pay attention to it, thus not taking your mind so seriously.
Worrying about the past or the future is futile because it doesn't exist, only the present moment exists, and when we realize this we can rid ourselves of a great deal of worry over things that are not real. If all there is is the now, then we realize that we really have nothing to worry about, because the beauty of the present and everything around us at that moment takes over, and we can free our mind from suffering. And because presence makes us more aware of our surroundings, we begin to appreciate nature more and experience joy in simple, everyday things, so that we no longer need to look to the future for pleasure.