Does the willpower fail, or is it the disconnect between willpower and action?
Just how do we define the will? Frankl, in the doctor and the soul, says the will is our ability to make choice, which is also what Epictetus suggest we have control over, absolutely. If the power to choose is really the soul, the geist, the mind, then when I overeat, there is a disconnect between the body and mind, for I am aware of doing wrong, but keep doing it regardless. I become possessed by a force outside of my mind, and my body just does it.
During meditation, I can separate my mind from body, I have control over the mind, but my body still wants and does. It is not, therefore, a willpower failure but a disconnect between mind and body that occurs.
In Sam Harris's work, he found nothing he could relate to as free will, but he was dependent on the body for measurement, so he was not isolating the will, but including the body/mind interface in what he was measuring. In order to make eating a fair choice, we need to provide an alternative to eating at all times. That choice must be as enjoyable and fulfilling as eating... well after our metered meal.
Retirement may be a bad concept, as one really needs something to do. In engineering, as a technical specialist, loss of memory or rather failing memory is not a good thing. Other professions may not be as heavily dependent on memory, but for my own safety and others, I need to give it up. Now I need replacement activities, but lack the desire and/or interest to do much. Oh well, in the end we all just die anyway.
So I guess this whole post is just about how wrong collective thinking about willpower failure is. It is the connection between will and physical action that has failed, and much of that is not through the individual, but through the collective thinking, education, we receive, informally.