That is absolutely correct. However the problem is that human's body needs energy to run - think, work, feel emotions. So if you can imagine someone on the bed 24/hrs a day, then indeed a simple calorie reduction will help. Because calories will be used for simple body functions, and not anything else. Restricting calorie intake for someone who has to go to work daily, work, live a life, will not work beyond certain limit, which actually allows to live that life.