Simple? Yes. Easy? No. And probably the method and mechanism in the second case (chemical dependency) will be different from those in the first case.
By 'simple' I mean that the method and mechanism is well known, scrutable to a reasonable adult without any special effort of mentation, and not requiring complex calculations, caveats, hidden factors, or other complications. Cold turkey is simple, but gradual weaning is also simple. But they are not easy.
I don't think it is that simple. The very fact that you have to suggest the possibility of weaning shows that there are factors that have to be taken into account beyond simple "willpower".
I suppose the question is whether or not your way of defining "simple" is in any way useful to anybody. You can say that the way to get over heroin addiction is by simply no longer taking heroin. I hope you would agree that even leaving the issue of motivation or willpower aside the either it's
not quite that simple, or that any conversation which boiled the problem down to just that was itself too simplistic to be of any utility to anybody, or to contribute meaningfully to any conversation about heroin addiction.
My thesis is that while weight-loss motivation is a complicated thing, the methods and mechanisms of weight loss are relatively simple: Eat less, exercise more. I am in disagreement with those who argue that the mechanisms and methods of weight loss themselves are complicated, or that a motivated person cannot make progress by implementing the two simple principles in their daily life.
I think that perhaps there's some kind of sliding scale of "complicated" here. I don't think that how food is converted into fat is the most complicated thing in the universe, but nor do I think it's the simple "the calorific content of food is the only factor involved" mechanism that you seem to be portraying it as that. The human body is a complicated collection of systems which react to each other and external stimuli in mostly predictable but not necessarily entirely uncomplicated ways, and not all foods are equivalent to all other foods.
I think there's a middle ground somewhere between "too complicated for human brains to ken" and "the only factor is the number of calories consumed".
I have no problem with your characterization of it being "a simple matter of willpower".
That's your characterisation, not mine.
But I am essentially arguing against the idea that we should tell people who have solved the problem of willpower, or who are trying to solve the problem of willpower, that they should not bother eating less and exercising more on account of how the methods and mechanisms of weight loss are too complicated for their motivation to make a difference in such a simple way.
So you're arguing against a straw man?
No, but I would say that overcoming an underweight condition due to anorexia was as simple as eating more. Possibly as complicated as ramping up food intake over time, and perhaps choosing specific kinds of food during the early phases. That's method and mechanism.
Right, so again the question is - is what you're saying actually in any way useful to anybody? Anorexics can just eat more, heroin addicts can just stop taking heroin, and people suffering from depression can just cheer up. Problems solved!