Well, obesity happens basically when you are overloading yourself with bad calories and sugars from constantly eating processed foods or foods that are high in sugar. So when that happens, your body will get used to having high levels of sugar in it and will crave it. When that happens, you will want to eat those kinds of foods in order to satisfy your cravings. You may want to cut down but you will keep on craving and eating and craving and eating. That is the vicious cycle of obesity.