The efficacy of a treatment, remedy, medicine and so on depends on the ability to take or tolerate it. As much as its actual potency or lack of it. If you cannot complete the course, then its obviously falling short and needs a redesign at least.
Nothing to do with morality. Anti-biotic medicines work the same on lawless as the law abiding. Those deemed good or bad. Nor does efficacy depend on being deserving or undeserving. If you break your leg messing about or in the course of saving puppies from drowning, the treatment is the same. Or according to the requirements of your injury.
Medical need is the only judge when it comes to medical matters. What's being said here is not that fat people can never become slim and stay that way. It's that weight loss dieting is intrinsically unsustainable for the overwhelming majority of people and that's a feature of the way our bodies function.
On the rare occasion that it is, it won't be down to greater or lesser "self control". Its a biological anomaly that cannot be generalized.
The famous 95% of weight loss diet fail is a probabilistic figure. Every attempt at dieting has a 95 % likelihood of failure. I don't think that means the same as out of 100 people, 5 will succeed at dieting. It means every time you diet, that's the chance you have of sustaining it to something approaching slimness-if you're fat.
Anyone could theoretically have a very small chance of success and a far larger one to fail at any attempt. It is possible for some element of spontaneous metabolic adjustment to make a difference at any time in any person, whether they diet frequently or not.
'Morality' is a total irrelevancy when it comes to a medical treatment.
This kind of thinking, plus such as, you have to be positive, if you don't believe you can't do it etc., is the hallmark of quackery.
We're told diets work if you 'stick' to them.
It happens that the lack of sticking to weight loss diets is a product of their intrinsic dysfunction. Even if this were not so, there has to be a realistic assessment of probable chance of any measure. Not pretence based on assumption.
Theoretical efficacy is just that, theoretical-unless it can be made actual. We have a whole raft of clinical trails and tests for medicines and other treatments to confirm hypotheses. When you want to change A and you apply agent B to it. The acid test is whether A changes (in the way you require).
If it doesn't, no excuses are needed, it doesn't work. Take it from there, find out why it doesn't work and that might lead to you find out how something else could. Or don't, it's up to you.