Sarah had a definition of willpower the today. http://everydaypaleo.com/sleep-mood-and-willpower/?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+EverydayPaleo+%28Everyday+Paleo%29
But I will provide a working definition: willpower is that rational conscious force that allows us to overcome habit, physical desires and cravings of the body or unconscious mind. It is a short term, rather weak force. Signaling from willpower is also weak. We need to pay attention to even pickup on it, unlike the scream of the unconscious or body. Many of us live in our unconscious, most of the time. Other defenses are also required, especially if food addiction, maladaptive eating behaviors, habit, environmental factors, physical issues that cause no satiation and poor food knowledge are present. Some things sold as food are just not food.
First willpower must be conscious and active. Do not expect to not eat and sit in front of food or where food is available. We need to eat, but is small amounts, with much work that we enjoy between. Eating cannot be a social activity, it is for energy collection only. This is a major attitude change for most of us, and will be resisted by the family.
Sitting where food is available will just grind on the mind until the will power is defeated. Getting up and go away may be the only solution. Then comes exhaustion and sleep.
But then, what do I know?